Your window AC is making noise? In this article, we’ll cover all the different noise types in window ACs. For each noise, we check whether it is dangerous, the cause for the noise, and, of course, how to fix it (if necessary).
Quick answer: Window AC noises are usually not dangerous. But scratching, whistling or banging noises indicate larger failures in your window AC which you have to address. The most common cause for window AC noises is broken parts in the compressor or fan, such as broken bearings or broken brackets which allow the fan or compressor to jump around in your window AC.
Summary of window AC noises
Let’s first have a look at the all different noises that window ACs make, their reasons, and whether they are dangerous.
After the table, you will find a fixing guide for each noise type.
| Window AC noise | Reason | Is it dangerous? |
| Humming noise | Compressor running or lose window setup | no |
| Rattling noise | Loose parts inside AC or in window setup | no |
| Buzzing noise | Electronic issue or stuck moving part causes AC power supply to overload | yes |
| Scratching noise | Internal friction in compressor or fan | no |
| Whistling / Hissing noise | Refrigerant leak | yes |
| Gurgling noise | Air trapped in condensate drain or refrigerant | no |
| Clicking noise | Thermostat switching power settings | no |
| Crackling noise | Parts expanding or compressing due to temperature change | no |
| Banging / Knocking noise | Compressor or fan broken | yes |
Causes and fixes for a window AC making noise
Let’s have a look at each window AC noise one-by-one. For each noise, you get an introduction, which helps you understand the cause of the noise.
And then, you get a way to test for the cause and how to repair it. If possible, I also append a section on how to prevent each noise in the future.
1. Humming noise
The most common window AC noise is humming. Humming is always a sign of vibration.
Since window ACs sit inside your window, the humming from the AC spreads over the entire wall and can even reach other rooms.
All window ACs (and ACs in general) have a compressor. The compressor liquifies gaseous refrigerant. The liquid refrigerant absorbs heat from your room, gasifies, and cycles through the compressor again. This process moves heat from your room outdoors.
Compressors are the loudest part of an AC. Unfortunately, they are also the most important part.
There’s nothing you can really do about the compressor noise. Normally, window ACs are relatively quiet. Many window ACs are only 52dB, which is comparable to a quiet refrigerator.
Humming noise can get very loud if the humming noise of your window AC matches the resonant frequency of your wall or window AC setup.
All objects have one frequency at which they begin vibrating uncontrollably. When you sing in the shower, you might notice that some tones sound “extra loud”. That happens when you hit the shower’s resonant frequency!
If your window AC hits the resonant frequency of your room, the walls, or the window, the humming noise amplifies.
So, the issue is not in the window AC itself. Which is a good thing and makes this problem easy to fix.
How to test
You can check resonance in your room in two ways. Either turn your window AC on and feel whether the window and the walls vibrate. Also, you can try to match the frequency of your window AC with your voice and see if your voice sounds louder.
( Better do this when you’re alone, otherwise, people will think you’re a maniac )
You can even cross-check whether your window AC hits your room’s resonance frequency by installing your AC in another window in another room. But this takes a lot of time and effort. Do it, if you can. But if you can’t, no problem.
How to fix
There are two ways to fix the humming noise of a window AC. First, you have to make sure that your window AC sits firmly in your window. There should be no space for it to shake around.
Many window ACs come with insulating foam tape. Use it! If you don’t have yours anymore, then get this insulating foam tape for ACs (click here to view it on amazon).
The tape, the walls, and the window will absorb all the vibration from your window AC.
Also, you can add dampening to your room. This can be a simple carpet on the floor or even soundproofing foam that you mount to your walls.
2. Rattling noise
Rattling always indicates loose parts hitting each other. Normally, all the parts in a window AC are fixed and don’t rattle around.
So, if you notice rattling in your window AC, it’s a surefire sign that something is going wrong.
Continuous rattling indicates that the cause is a moving part in your window AC. The only moving parts in an AC are the compressor (which compresses the refrigerant), and a fan (which blows the cold air into your room).
So, let’s check the compressor and the fan.
How to test
To test and fix the rattling noise, you have to unmount your window AC. First, you can verify that your window AC rattles, by shaking it.
Window ACs are heavy, so, unless you’re a powerlifter, you likely won’t shake it in the classical sense. But you can place the window AC on one edge and tilt it back and forth.
( Drain the water pan before )
Listen to whether you hear any loose parts clanging against each other. If you don’t, place your window AC on another edge and try again.
If you hear something, you know for sure, something is off.
Open the case of your window AC until you see the fan. Ideally, you should also open everything until you see the compressor.
Then, turn it on. Be careful, since some window ACs have exposed power electronics. So, don’t get too close to them.
Listen to where the rattling in your AC comes from. There are now two possible outcomes:
Either you hear the rattling, which helps you track down the noise until you find the faulty part.
Or you don’t hear any rattling now that your AC stands on firm ground. This means that the cause is not a loose part, but a loose window setup.
How to fix
Locate the broken part (if there is one). Likely it is the compressor or the fan. Usually, it’s easy to replace a broken fan. Just buy a similar fan online or in a hardware store and replace it.
This might need soldering. But aside from that, there are no difficulties.
If the rattling comes from your compressor, find out whether the compressor rattles as a whole, or whether it rattles from its inside.
If your compressor rattles as a whole, this means your compressor does not sit tightly. You might need to screw it in tighter. Or you can dampen the rattling with sponges you place below your compressor to hold it upright. Ideally, test this before you reinstall your window AC and make sure the compressor does not get hot.
If the compressor rattles from its inside, then I recommend just getting a new AC. You can sell your broken one.
Check out my review of my favorite air conditioners
3. Buzzing noise
Buzzing noises are always related to electronics. The classic buzzing sound comes from AC currents or voltages creating vibrations. Usually, the frequency of AC current is 50-60Hz, which, usually, causes a buzzing sound of a matching frequency in the power electronics if there is a fault.
When your window AC is plugged into the wall outlet and running, the power from the wall outlet powers all the components of the window AC.
However, when a component breaks, the power has nowhere to go, which creates the buzzing sound.
One usual cause of AC buzzing is when the compressor is stuck and does not move.
This can happen when you don’t use the AC for a long time. Or when bearings inside the compressor break.
Another similar cause could be a stuck window AC fan.
Technically, other broken parts can create a buzzing as well. But the compressor and the fan are the only moving parts in a window AC. So, they are the only parts that wear down over time.
So, they are the most likely points of failure.
How to test
Turn on your window AC. Does it blow air? If yes, then the cause is not the built-in fan.
Is the air coming out of your window AC cold? If yes, then the compressor likely also works.
If either no air comes out of your AC or the air coming out of it is not cold, then either your fan or compressor is broken.
But if your window AC is working fine and still creates a buzzing noise, then the issue must be in the power electronics.
How to fix
Unplug your window AC and open its case. If your fan or compressor is the cause, check them for dirt. Dirt can clog them and prevent rotation. Clean your compressor and the fan.
Also, check the bearings of the fan and the compressor by manually trying to rotate them. They should turn smoothly.
If your fan’s bearings are broken, you can usually replace the fan. Just buy a replacement online or in a hardware store.
Replacing compressor bearings is harder since disassembling a compressor requires special tools. And also, many manufacturers don’t sell replacement bearings.
So, you are pretty much left with either replacing the entire compressor or the entire window AC. ( I recommend the latter )
If the source of your buzzing is not the fan or the compressor, it is very likely somewhere in the electronics. If you are familiar with electronic repairs, have a look at the electronic circuitry and see where the buzzing originates.
Then, visually check whether you see any blown or broken-off parts. If you manage to locate the issue, replace the part with an identical one (this might need soldering) and try running your window AC again.
4. Scratching noise
Scratching noise is always a sign of aggressive friction. Again, since the only moving parts in a window AC are the built-in fan and the compressor, we only have to look for the cause there.
Electronic circuitry obviously does not move and, therefore, does not scratch anything.
One unlikely, but possible, cause, could be small animals inside your window AC.
Last summer I started noticing a scratching sound coming from our roof. I live on the top floor below a pitched roof. The first day I assumed it must be the wind.
However, the scratching continued for days and I could not figure out what it was until I saw hornets flying in front of the roof window.
So, I punched against the wall, and a whole swarm of hornets flew out the roof!
The hornets were trying to build their nest in the wooden roof structure and scratching the wood, which was very loud considering how small those animals are.
How to test
Does your window AC create a scratching sound even if it’s turned off? If yes, then assume there are bees, wasps, hornets, or whatever other nasty little beasts inside.
You can punch the window AC where the scratching noise comes from and see whether the scratching changes.
It might get stronger or stop entirely. Or a few flying friends might leave your AC to see what’s going on.
If the scratching noise only occurs when your window AC is running, then the issue is either in the compressor or the fan.
How to fix
To remove insects, use an anti-insect spray. Carefully open the window AC’s case and see if there is a nest inside.
Depending on the laws in your location you can remove the nest yourself. Either carefully remove it and relocate it to nature. Or spray-destroy the nest. It’s your choice.
And some states and countries have laws prohibiting the self-removal of insect nests. But nobody can really enforce it.
For the future, make sure that all air filters are tight and have no holes, so the chance of insects entering your AC decreases.
If the scratching noise comes from your fan or compressor, you will have to replace the fan or compressor (as described in the previous sections already).
5. Whistling or hissing noise
Whistling or hissing noises are usually a sign of refrigerant gas leaks. But sometimes the whistling can also be a capacitor failure.
Let’s have a look at both cases.
Gas leaks are, basically, gas passing quickly through a crack or a loose connection point in a pipe. The gas passing through the pipe creates a high-pitched whistling noise because it excites vibration in the pipe.
It’s like whistling with your mouth where you form a narrow air opening with your lips. The air passing through the opening excites vibration in your lips.
Capacitors can also whistle when they break down or when other parts that they are connected to break. This can create high-frequency voltages which cause the capacitor to vibrate and whistle.
How to test
To test for these causes, open your window AC. Try to locate the whistling or hissing sound. Does it originate from the pipe or from the electronic circuit boards?
How to fix
You can’t really quick-fix a leaking pipe. There are some AC leak sealant products online, but I would not trust them.
Ideally, you should get a replacement pipe. To do it, you have to suck out the refrigerant, replace the pipe, and then recharge the pipes with refrigerant.
To me, this sounds very troublesome. And I’d for sure cause more damage than repair anything. At this point, your best choice is to just get a new window AC.
Window ACs cost less than a window AC repair. So, just replace it. Scrap dealers will usually happily buy your broken window AC!
If the cause of the whistling or hissing is a broken capacitor, then replace it with an equivalent replacement capacitor. This requires soldering. If you can’t solder, just get a new AC.
6. Gurgling noise
Gurgling noises are always a sign of bubbles moving around and popping in liquids. Gurgling noises can, therefore, originate in two components of your window AC.
The most likely cause is in the water drainage. Trapped air in the water ducts causes a gurgling sound.
The gurgling sound can also come from the refrigerant duct system. Either air somehow got into the ducts. Or the refrigerant causes a gurgling sound on its own (refrigerant gas in refrigerant liquid).
How to test
Here you can only open your window AC’s case and try to listen to where the sound comes from.
Also, if you have a water drainage system, you can try to run your window AC without the water ducts attached. Instead, drain the water directly into a drain pan or a bucket.
This way you can tell whether the gurgling comes from the water drainage, or from somewhere inside the AC.
How to fix
If the gurgling comes from the refrigerant ducts, you can hire a professional to vent the ducts. Also, check whether there is any leak in the ducts. The air came from somewhere. And it can’t magically pass through metal pipes.
If, on the other hand, the gurgling comes from the water system, drain all the water from the pipe. To be sure, also clean the ducts using a pipe brush.
You can use this drain brush (click here to view it on amazon). With 67 inches, it should be long enough for most window AC drainages (at least on the first floor). If you need any longer than that, get a longer drain brush, or disassemble your water drainage and clean the individual ducts separately.
7. Clicking noise
There are several possible things that can cause clicking in a window AC. Clicking always happens when one piece quickly snaps into another.
The clicking could be a relais switch in the electronics. Or it could be a mechanical part that clicks against another.
I just boiled myself a kettle of water where I noticed two clicks: The electric kettle clicked once when the water boiled to shut off the heating. And it clicked a second time when it cooled down.
The temperature sensor is a bimetallic piece that bends and contracts upon temperature change. It could be that some ACs work similarly.
Anyways: Clicking sounds always occur when some state in electronics change. Window ACs click, when the thermostat turns on or off the cooling.
One typical sound is that of a clicking relais switch. A relais is an electrical switch which, when you apply voltage, attracts a metal piece magnetically, which, in turn, snaps into the circuit and closes it.
So, usually, clicking sounds are normal and expected in a running window AC.
Oftentimes, temperature change in the AC’s parts causes them to click against each other as well. This is usually the case shortly after turning the AC on and shortly after turning it off (when the greatest temperature changes occur).
There’s one more possible source of clicking: Shortly after installing your window AC, the walls and the window frame and the structure holding the window AC in position have to adapt to the added weight.
This can cause an occasional click, even when the window AC is turned off.
How to test
If the clicking only occurs when the window AC is running, it is likely only the switching sound of the thermostat. So, that’s nothing to worry about.
Even after an hour of running, a window AC can click when it senses your room is cold enough and switches off the cooling.
If, on the other hand, your window AC clicks only shortly after turning it on or off, then the temperature changes cause the clicking sounds. That’s also nothing to worry about.
Lastly, if your window AC clicks when it is not running, the clicking can come from the added weight to the walls and window frame, which have to adapt.
How to fix
You don’t have to do anything if your window AC only clicks when it runs. Clicking up until 5 minutes after shutting it off is acceptable as well since some parts need time to expand.
If your window AC keeps clicking while turned off after installing it, try adding some support to hold its weight. For example, you could place a pedestal, table, or stool below the window AC. And then add some books to fine-tune the height.
Of course, that’s not a real solution, but it helps you figure out whether the lack of support structure is the source of the clicking.
If you find it is, add real support using this window AC support bracket (click here to view it on amazon).
8. Crackling noise
Crackling is usually a sign of parts contracting or expanding due to temperature changes. Whenever I turn my portable AC on, it crackles occasionally for a few minutes. This is due to the case and the internal AC parts adapting to the new temperature.
Crackling can be very present in ACs since the internal components in an AC are exposed to large temperature gradients.
The cold air coming out of a window AC can be as cool as 64°F (18°C), while the back part, containing the compressor and the refrigerant gas which absorbs the heat, can be up to 104°F (40°C) or hotter (depending on the outdoor temperature).
So, whenever you turn on your window AC, you create this 40°F temperature difference. Some parts cool down (contract) and some parts heat up (expand).
It takes some time for the parts to settle and adapt to their new size, which the occasional crackling sound shows.
You find crackling sounds in all HVAC devices, not just ACs. All my space heaters crackle after I turn them on.
So, the crackling is nothing to worry about, except:
The crackling should only occur shortly after turning your window AC on. And it can occur after you turn your window AC off.
But if your window AC crackles continuously, there might be another issue.
One possible reason could be unstable components that change temperature frequently and don’t settle for an equilibrium temperature. This indicates an error in the thermostat control design.
Usually, this happens with very cheap window ACs, or when the temperature sensor is badly calibrated or broken.
How to test
Turn your window AC on. If your window AC crackles only shortly after turning it on or off, there is nothing to worry about.
If your window AC crackles continuously, the thermostat control mechanism is likely broken or poorly calibrated by the manufacturer.
How to fix
You can’t really fix the crackling. Technically, it is not dangerous and, as long as your window AC works fine otherwise, the crackling is a mere inconvenience.
It just shows that the internal temperature is not stable and changes occasionally. If you are sick of your crackling window AC, get a new one!
Most window ACs don’t crackle beyond a few minutes after turning on.
9. Banging or knocking noise
When there’s a banging or knocking noise coming from your window AC, beware! Aggressive banging or knocking is always a sign that some part broke off.
A one-off knocking sound means that some part broke off. However, a continuous banging noise is a sign that a rotational part (either in the fan or in the compressor) broke off and keeps moving!
Continuous banging is more dangerous than a single knocking sound.
In both cases immediately shut off your window AC and stop using it until you know exactly what the problem is.
How to test
Shut off your window AC. Open the case and see whether you can locate any broken parts.
How to fix
Inspect the area surrounding the broken part. Is it just a broken-off plastic fan blade? Then, you can replace the fan.
However, if the entire compressor broke off and caused the banging sound because it jumped around inside the window AC case, destroying all the electronics, then you have no choice other than replace your window AC.
Quality window ACs never produce banging or knocking sounds. Banging and knocking are signs of severe quality control issues. I recommend replacing your window AC with a quality brand product.
What to do if your window AC still produces a noise?
If you tried all the fixes and your window AC still produces a noise you are uncomfortable with, then I recommend just getting a new AC.
Window ACs are the most cost-effective ACs, and they won’t break the bank.
I highly recommend this 10,000 BTU Midea window AC (click here to view it on amazon).
Midea is a brand I (and many others) trust. This one won’t produce any weird noises anytime soon!
Please note that this model is a 10,000 BTU model. The BTU rating depicts the cooling power. For balanced and low-noise cooling, you should get the right size window AC for your room.
A rule of thumb is to get 40 BTU of cooling power per square foot of room size. So, if your room is 200 square feet, then get the 8,000 BTU option. (40 BTU × 200 sq. ft. = 8,000 BTU).
Getting the right size is important. A too-small window AC will not cool your room properly. And a too-large AC will cool it too much, then make a long pause, then cool again (so, it will switch the cooling on and off frequently, instead of supplying just the right amount of cold).
Also, powerful ACs tend to be louder.
Conclusion
That’s it! I’ve listed all the noises I could think of and all the ways to fix them!
If you could not find your noise in the list, or you are not able to fix your AC noise issue, then just get a new AC.
Oftentimes, the time and effort it takes to repair something are not worth the cost of a window AC.
So, instead, you can just get a new device.
This way you don’t have to worry about something breaking anytime in the near future. And you have a new and fresh window AC for the next decade to come.
But if you manage to find a noise cause in your window AC that’s not listed in this article, please tell me your story via mail and I’ll be happy to include your experience here!