HVAC Noises Explained

Squealing, Hissing, Clanking and Other HVAC Noises Explained

Your HVAC system is a powerful machine that delivers conditioned air to every corner of your home. Naturally, it’s going to make some noise. The gentle whoose of a manufactured breeze can be a kind of soothing white noise, which makes unexpected sounds so jarring.

Here are five common noises and their causes.

Squealing or screeching

That high-pitched whine or squealing could be one of two things: If you have an older, belt-driven unit, it’s likely one of the belts is worn or misaligned. Newer HVAC systems, however, do not have belts. Instead, a direct-drive motor propels a fan to draw air across condenser coils. In this case, you could chalk the screeching up to worn bearings. In either scenario, the noise isn’t going away on its own. Get this fixed ASAP to avoid more costly repairs down the line.


A persistent hissing while your AC is running could indicate a major problem or a minor one.

Major problem: There could be a gap in the ducts, especially if you hear hissing coming from a wall. Don’t ignore this. Leaking ducts means conditioned air is escaping to parts where it’s not needed. This forces your air conditioner to work harder to reach your set temperature, resulting in a steep hike in your electricity bill. A professional HVAC technician can inspect your ducts and have them properly sealed.

Minor problem: Are you sure you have the right size filter for your unit? If a filter isn’t sitting right, then air is leaking through a gap in the seal. Simply replace it with the correct filter size. Problem solved.


Somewhere within the system a part has come loose or the indoor blower or outdoor fan blades are out of balance and knocking against other parts. It’s annoying and it’s only going to get worse if it isn’t addressed by an HVAC technician.


That click you hear when the air conditioner kicks on and turns off is normal, but if it persists, there’s a problem. Frequent clicking could be a sign your thermostat or other electrical component is on the fritz. This sound typically precedes a total HVAC breakdown, so schedule an appointment right away.


This is your HVAC unit’s anguished cry for help. Screaming or high-pitched whistling could mean that the refrigerant is leaking or there is excessive pressure within the compressor. A sensor should trigger the unit off when this happens. It’s not going to turn on again until you get it fixed.

You don’t have to wait for audible cues that something is wrong. Preventative maintenance will help your HVAC system operate quietly and at peak performance. To schedule a tune-up or to become a member of our Complete Comfort maintenance plan, call 317-671-7552.