How to Interpret Different AC Noises

Learn how to interpret various AC noises and their implications. Trust Sandium for expert furnace and AC unit repair services. Ensure best air conditioning service with us!

Updated on Oct 22, 2023
5 min read
How to Interpret Different AC Noises

All home appliances and systems make some noise. However, there may be a cause for concern if your HVAC system is making funny or unnatural sounds. It is best to have your system checked out by a Bay Area professional if you are not sure what to do. This article talks about possible causes that may be making your HVAC system produce noise.

Screeching or Squealing

This kind of noise can be because of a problem with the fan belt in the blower. The belt probably needs to be replaced. The sound also refers to the motor needing lubricant. You may be able to do this on your own depending on the make and model of the furnace.

Thwapping Sound

This usually happens when there is something stuck in between the fan blades of the blower. There is an easy way to tell the problem if the noise comes and goes with airflow. The obstruction may be causing unnecessary wear and tear even if it is not critical to the furnace’s ongoing functioning.


This is an unnaturally common noise to come from an AC unit. It usually represents a compressor malfunction. Buzzing may also be caused by a refrigerant leak that makes the unit freeze. It is possible that there is a loose part vibrating that needs to be checked out.

Frequent Clicking

Frequent clicking is usually because of something wrong with the inside air handler or the outside compressor. Clicking from the furnace could be a sign that the electronic ignition or pilot light is malfunctioning.


Booming sound generally occurs when the furnace attempts to light unsuccessfully from an electronic ignition or pilot light. This causes a gas buildup in the combustion chamber that tries to ignite all at once suddenly. You should call an HVAC technician because this is not a desirable situation. The problem is usually because of a carbon particles build-up. You should have the flue chamber inspected and cleaned by a professional.

High-Pitched Screaming or Whistling

You need to act quickly and turn off the unit immediately. This is a warning sound. You should not attempt to start the system till you can get help. High-pitched whistling or screaming signals dangerously high refrigerant pressure as well. It may also mean the compressor is failing. You should seek professional help if you are facing this problem. Refrigerant leaks are dangerous. You should not turn the unit back on till it has been repaired.


The hissing sound may be coming from the AC compressor or the furnace. If the AC compressor is making the hissing sound, it may mean an internal refrigerant leak. This could be because of dangerously high levels of internal pressure. You should immediately disconnect power and call a technician.

If the hissing is coming from the furnace, you should have the air duct checked. This will require professional repair. In some cases, the sound comes from the furnace itself because of a leak that should be looked at by a technician.

Rattling From Fan Unit

Rattling is a common HVAC noise. It may be because of compressor wear and tear. It could also be because of failing bearings or a worn-out clutch on the compressor.

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