End of Season Sale - Save up to 15% off new AC units with 10 year parts & labor warranty included!

One of the worst feelings in the world is to turn on your AC on a hot day and hear something you’ve never heard before. A harsh clunk or shrill squeal has you in a panic because you have no idea if your AC is about to quit working. Before you get too worried, here are some of the common noises and what they mean.

How Your AC Unit Works

Before diving into the different sounds your system makes, learn how an AC system works. It can help you better understand why certain noises occur and what those noises mean the system is doing.

Any air conditioning system has three key components. There’s a compressor, a condenser, and the evaporator coil. The compressor and condenser are located outside in a unit that’s near your home. The evaporator is inside and connects to ducts that travel throughout your walls, basement or crawl space, and attic. Everything starts with Same Day Service that travels through these three components.

  1. The Compressor: Start at the compressor. It pressurizes the coolant while heating it up. The compressor’s pump pushes the coolant through copper tubing to the condenser. 
  2. The Condenser: The condenser coil turns that coolant into liquid and sends it inside the house to the evaporator coil. It’s also here that the heat from inside the home is released from the coolant and into the outside air using fans.
  3. The Evaporator: The cooling process really starts at the evaporator. The heat within the liquid coolant dissipates due to evaporation. A fan, also known as a blower, blows air across the evaporator coil, pushing cool air into the ducts and the home. The now-cooled Same Day Service collects heat from inside the home and brings it back outside to the compressor where the process repeats. 

All three of these components have mechanical parts like pumps and fans. As the components start up or shut down, there are noises. Typically, you won’t hear much more than a hum or quiet fan, but sometimes an older system will start to make noise.

Understanding the Noises Your AC Makes

Now that you know the basics of how an AC system works, what are some of the noises you’ll hear? How do you know if the noise is a warning sign or not?

Banging, Clanking, and Rattling Sounds

Rattling can be created if items like sticks or built-up dirt get into the outside system. While you want to keep shrubs and trees away from your AC compressor and condenser’s outside unit, you can’t avoid everything. Wind gusts can blow leaves, twigs, and sticks quite a distance. This is something you can fix yourself. Inspect the system and clean it out if needed. If the sound goes away, you’ve taken care of it on your own. If not, it’s time to have a professional come look at your system.

Clanking noises can be tied to fan blades that are out of balance. If something has caused the fan blades to become dented or they’re loose, they’re going to make clanking noises. Don’t ignore this noise.

It could be that a screw or screws have loosened and components within the fans are starting to shake and rattle. If this is the noise you’re hearing, call a technician. You want to have it assessed before it rattles so much that a part breaks off or becomes bent. The same is true of banging. Your system shouldn’t make banging noises. If it is making a lot of loud banging noises, it could be time for a new system as the components within the compressor are wearing out and loosening up with age.

Bubbling or Dripping

Are you hearing a bubbling or dripping noise? If the drain pipe on your outside AC unit is blocked, you will hear a bubbling noise. The unit must be disassembled to find and clear the blockage. The same is true of a dripping noise. If the drain pan is filling up with water rather than draining properly, there’s going to be a dripping sound. It’s important to have your AC unit inspected and cleaned.


Buzzing noises are usually linked to ice build-up on the coils. Turn your system off for a while and let the ice melt. This is only a temporary fix, as you need to figure out why the ice build-up occurred. Change your filter and see if that helps prevent ice build-up. If you haven’t had your system cleaned in a while, it’s time.

If that doesn’t fix the noise, it’s likely something electrical. Don’t risk an electrical fire. It could also be related to loose fans that aren’t spinning properly. Call an AC technician for a diagnosis. If repairs are needed, it’s better to have this taken care of ASAP.


You will hear a clicking noise when your AC first turns on and off. This is the noise the thermostat makes when it starts up or reaches temperature and shuts off. If it is happening continuously, your thermostat may need repair or replacement as it’s a sign that the thermostat isn’t registering temperatures correctly.


Are you hearing a hissing noise? Check your ducts for leaks. You may find that one room is not cooling down properly. That’s a clear sign of leaking ducts. Hire a professional AC team for duct sealing. Duct sealing is not a good DIY project. If you mess up, it can lead to costly duct replacements.


When your thermostat realizes your home is getting too warm, it triggers the relay switch to start the condenser’s motor. If the relay switch is bad, you’ll hear the buzzing when the condenser won’t start, so your home isn’t going to cool down. Humming is one of the noises you can’t ignore.

Squealing and Screeching

When your fans are having problems, you’ll hear squealing or screeching. It’s the kind of noise that can keep you up at night. Often, it’s caused by a bad bearing in the motor. It’s important to have this noise investigated, as the fans are essential to the proper cooling of your home.


Whistling is usually tied to airflow in the ducts. Air is now flowing correctly. If you have dirty filters or a blockage, you may hear the whistling. Try to fix this problem yourself by checking the filter. If it’s pretty dirty, replace it. This should stop the whistling noise. If it’s still there, you could have a clog in your ducts. For that, you’ll want to call in the professionals.

Get peace of mind with a free assessment of your air conditioning system’s health. Our technicians can look it over, see if there are potential issues, and let you know what it will take to repair it and have it running as good as new.

Is it time for a new air conditioning system? At All Year Cooling, we offer same-day installations. You will not be waiting days or even weeks to get your home cool and comfortable. If you do need your central AC system replaced, ask about our 10-year service warranty that protects you from unexpected repair costs for a full decade. Call, text, or chat with us online to schedule a professional AC consultation.

All Year Cooling