Your air conditioner unit is meant to make your home comfortable and be relatively low maintenance. Normally, you don’t even have to think about your AC, aside from the occasional thermostat adjustment. This is because most modern HVAC units now include technology that dampens the sound of the HVAC unit while it’s working, ensuring the noise level stays manageable.

However, if your air conditioner is making noise before, during, or after it completes a cooling cycle, that could be an indication to there is something wrong with your system.

We outline 9 of the most common noises an air conditioner may be making, what they could mean and how you can fix them. Hint: you should probably call the pros at One Hour Heating & Air Conditioning when you first hear any unusual noise coming from your HVAC unit.

What Noise is Your Air Conditioner Making?

There are several common (and a few uncommon – but noteworthy) noises that an AC may make.

The 9 Most common noises an air conditioner makes are:

  • Squealing/Screeching
  • Rattling
  • Buzzing
  • Clicking
  • Hissing
  • Whistling
  • Humming
  • Cracking
  • Banging

Why Is My AC Making a Loud Noise?

Now that you know the most common noises an AC may make, it’s important to understand what each noise may be caused by and how dangerous (or expensive) the issue could be.

Below, we outline each noise, the common causes behind them, and when it’s appropriate to conduct a DIY fix versus when you should call in the professionals.


Squeaking, squealing, screaming, or screeching noises could be an indication of bad fan motor bearings or a fan belt being either worn out or broken.

It could also mean that pressure has built within your compressor or that there is a potential refrigerant leak.

High internal pressure within your compressor will normally trigger a sensor, causing your air conditioner to shut itself off automatically, but these sensors are not error-proof.

In any of these cases, immediately turn off your air conditioner and call a professional. If there is a substantial amount of pressure built up in your compressor, it could lead to disastrous results, including a potential explosion. In addition, refrigerant is a hazardous material that not only threatens the health of your family but could cause irreparable damage to your air conditioning system.


Your air conditioner is made up of numerous components and sometimes those components come loose. When that happens, you will often hear a rattling noise indicating that the loose piece is being tossed around inside of the unit.

Common components that come loose include fan blades, cover plates, and screws. When these items are loose in your unit, it is common that you will hear a rattling or loud banging noise coming from your AC.

Additionally, if your unit has not been cleaned and you haven’t had an annual maintenance check-up, the rattling or banging could be caused by external debris finding its way into your unit.

Items like leaves, sticks, and even dirt particles can get stuck in the condenser, causing your unit to rattle or bang. If you are comfortable with cleaning your unit, you can remove the condenser cover to remove these items. However, if you have never attempted this before, your best bet is to call a certified HVAC professional.


If you notice a loud buzzing noise coming from your outdoor AC unit, there could be a number of culprits causing this noise.

Obstructed Copper Lines

If the copper lines connected to your air conditioner are obstructed or if they are touching each other, they can cause a buzzing sound. Ensure that your lines are insulated or padded to reduce metal-to-metal contact.

Faulty Capacitor

The capacitor in your AC system is responsible for storing energy to power your outside unit. When the capacitor goes bad, it will lack the energy to power the fan from turning on, which, in turn, will cause the unit to buzz. Call a certified HVAC technician who can properly inspect your unit and let you know if your capacitor can be repaired or if it will need to be replaced.

Contactor Malfunction

The contactor on your AC is what controls the flow of electricity to your compressor. As the contactor wears down, you will likely hear a humming sound coming from the defective component. If left unchecked the contactor, which when malfunctioning will prevent the unit from starting up, will cause a loud buzzing noise.

Isolation Feet

Your AC unit’s compressor has small rubber feet, called isolation feet, that often deteriorate after years of use. When those feet crack or break, the compressor will lose balance and begin making a buzzing noise.


There are multiple reasons an AC may click. The first, and most common, is not something to worry over. When the air conditioner turns on, if you hear a single click, there is no real need for concern it is generally the thermostat and the HVAC system talking to each other.

However, if there are multiple clicks or the clicking sound gets louder, there could be a couple of possible issues.

Fan Obstruction 

When there is debris or other components in your unit and the fan blades strike the obstruction, it can cause a clicking sound that will start slow then get faster and louder. If you are familiar with cleaning your outdoor unit, you can lift the cover and remove the debris to eliminate the sound. Otherwise, call a professional to safely remove the obstruction and perform an inspection on your system to ensure that the fan was not damaged.

Electrical or Compressor Issue

In addition to a fan obstruction, two additional issues that could lead to a clicking noise include electrical issues and compressor glitches. If you hear a clicking noise and your air conditioner doesn’t turn on or if you hear the noise coming from outside of your home, call a professional HVAC technician immediately to assess the problem.


A hissing noise coming from your AC unit could be signaling that you have a refrigerant leak. Refrigerant is the chemical your unit uses to keep the air in your home cool. If you hear a hissing and notice that your AC isn’t adequately cooling your home, chances are a leak is the culprit.

Because refrigerant is a controlled chemical that is highly dangerous, it is imperative that you call a licensed HVAC professional immediately to inspect your system and diagnose the problem.


Similar to the hissing noise, a whistling noise is not a good sign. This generally indicates that there is a refrigerant leak in the line. Turn your air conditioner off immediately and contact an HVAC technician to come out and conduct a diagnostic inspection of your AC system.


If you are hearing a light humming noise emanating from your AC unit, chances are that this is totally normal. Your air conditioner system is mechanical and, as such, will usually have normal noises that indicate it’s working – including humming. A light humming noise coming from your AC unit is actually the least concerning of all the noises on this list.

As with everything else, there is a “but.” If you notice your AC unit’s humming is louder than normal, it could be a sign that something within your unit is loose. Loose components in your system can lead to costly repairs in the future, so if you hear an unusually loud humming coming from your AC unit, play it safe and call a professional HVAC technician to diagnose the problem.


If you hear the sound of cracking coming from your air conditioner, chances are your unit has frozen over and the sound you are hearing is the ice cracking as your AC attempts to cool your home. This often happens when you have set your temperature too low and the additional moisture causes your coils to freeze.


Finally, if you hear a banging when your air conditioner starts up, this could be the sign of a broken compressor or a broken or imbalanced fan motor.

While fixing or replacing these components can often be costly, there are many considerations when deciding whether to repair or replace your air conditioning unit. Here is a six-question quiz that can tell you what your best option may be.

Woman At Home Plugging Ears

How to Fix Your AC if it is Making Noise

While some of the issues outlined above may be solved by conducting a DIY clean of your outdoor unit, the majority require the trouble-shooting knowledge and expertise of a licensed, professional HVAC technician.

While you should immediately call an HVAC technician to run a diagnostic on your outdoor system when you experience any of the AC noises covered above, if you are simply looking to reduce the regular noise of your air conditioner unit, we have a few options that may work for you.

Reduce Noise Outside 

Sound Blanket

When you hear the term “sound blanket” you may imagine an outdoor air conditioner cozied up inside a fluffy throw. While we love the idea of a comfortable AC, the sound blanket is actually placed over the compressor to stifle the sound created just by doing its job.

Sound Wall

A second option is to create a safe barrier between your outdoor AC unit and your home by building a fence that muffles the sound of your air conditioning unit. Not only does this dampen the sound of the operating AC unit, but it also keeps debris from entering the unit and has an appealing visual for the home.


One additional option when looking to decrease the noise of your outdoor AC unit is to plant shrubbery to surround your air conditioner. However, be sure to have a landscape upkeep plan in place to ensure that leaves, sticks, and dirt from the shrubbery don’t enter the unit and cause more problems.

Reduce Noise Inside

AC Placement

If you have the luxury of deciding where your air conditioner is placed, it can help reduce indoor noise by placing your unit away from living areas like your living room, bedrooms, and patio. You also want to choose a location that will not reflect the noise from your AC unit, such as brick walls. Areas with reflective surfaces can amplify the sound of your unit, causing the noise in your home to increase.


Add a mat that can absorb vibrations and sounds from your attic unit. This will limit the amount of sound heard inside your home.

In addition, cover the air ducts with sound-absorbing foam to cut back on the noise carried into your home.

Call the Experts

If your air conditioner is making any of these noises, it is best to consult with a trained, certified HVAC technician to pinpoint the issue and offer you the best advice for fixing the sound. Be sure to call the experts at One Hour Heating & Air Conditioning whenever you need fast, reliable service.