HVAC Noise: What Is And Isn’T Normal

You should expect some sound from your heating, ventilation, and air conditioning (HVAC) system.  However, some types of HVAC noise are a sign that there is an issue which could require professional attention. Knowing the difference can help you determine if you need to schedule a visit from one of our technicians.

Normal HVAC Noise

These sounds are common for functioning HVAC systems:


A steady blowing noise is the sound of air flowing through your ductwork. In most cases, this should be quiet enough that you only hear it if you are trying to. Otherwise, it will generally fade into the background.


Every heating and cooling system makes some noise while it is operating due to the many moving parts. This is softer for newer, more efficient units, but may be a little louder if you’ve had your system for a long time.

Start-Up Sounds

When you turn on your air conditioner, it will usually make some noise while the many different parts begin working.

Sounds That May Be Normal or Abnormal

These sounds may be normal, but could also be a reason to call a professional depending on the circumstances:


Metal ductwork naturally expands and contracts as the temperature changes. Popping is usually normal if it happens when you first turn your heater on or if it is only coming from the ductwork occasionally. However, you should get your system inspected if the noise is very loud, doesn’t stop, or comes from somewhere other than your ducts.


You should expect your HVAC system to click when you first turn it on or off, as this is the sound of the different parts either starting to move or coming to a halt. However, constant clicking or very loud clicking from your indoor unit can be a sign of an issue with your capacitor.


Older units may squeak when they start up. This is less frequent for newer systems. The best rule of thumb for this is to call a technician if this type of HVAC noise is not common for your particular unit.

When to Call an HVAC Technician

If you hear any of these sounds, you should schedule an appointment with an HVAC company:


A high-pitched screaming or whistling sound is a bad sign and if you hear it, you should turn your system off right away and call for emergency AC repair. This can indicate a refrigerant leak or a build-up of pressure within the unit.


Buzzing can indicate a compressor malfunction or a loose part. A professional can find and fix the cause of this noise.


If you hear a hissing sound inside your AC compressor, it could be a refrigerant leak. In this case, it is best to turn the unit off until it can be inspected. If the sound is coming from your furnace or ducts, it could be an air leak. Either way, an HVAC technician can help.

HVAC Repair in Tucson, AZ

There are many other sounds you might hear from your unit such as banging, rattling, or thumping. When in doubt, it’s a good idea to schedule an appointment just to make sure everything is working the way it should. At Signature Heating and Cooling, our team is available 24/7 for emergency repair. We will work to get your system up and running quickly so you can stay comfortable during the hot Tucson summer.

If you are noticing any unusual HVAC noise, contact us today.
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