Weber County
Brigham City
Salt Lake


If you depend on your HVAC system to keep you comfortable night and day, you may know how unpleasant and nerve-wracking it is to hear a loud clunking sound from your AC unit just when you're settling down to sleep. Here are a few common reasons why your HVAC system may be making abnormal sounds.

1. Mechanical Breakdown

Your AC unit works very hard in the summer, and its functioning can go wrong in several ways. For example, moving parts such as fan blades can come loose inside your outdoor unit and start banging around, or some large twigs or other debris could fall into the unit and get noisily beaten up by the fan.

Another potential issue is that your unit could be working too hard. This could cause the coil to freeze up, which reduces the effectiveness of the unit and causes it to run constantly. A constantly running unit may be less noticeable than other abnormal sounds, but if you notice that your unit never seems to take a break, something is probably wrong.

If you notice a loud or abnormal sound coming from your outdoor unit, immediately shut it down and call a technician. These issues can range from mild to quite serious, so get a diagnosis right away, and don’t use the unit in the meantime.

2. Rodent or Roach Invasion

Small insects such as ants typically don't tend to make a lot of sound if they invade your HVAC system. However, it's also common for mice, rats, bats, or cockroaches to show up inside your ducts. These types of pests can make enough noise to be heard, especially at night when the house is quiet. They can also cause serious electrical problems and health risks.

If you hear scuttling sounds or scratching in your walls or ducts, a pest problem could be the issue. Roaches will probably only make small scuttling sounds (possibly amplified by the ducts themselves), but rodents may make scratching, chewing, and even squeaking sounds (or, in the case of bats, chirping sounds).

If you suspect pests in your ducts, do not spray poison inside — it will simply blow back out into your living space. Instead, have an exterminator remove the pests professionally and then have your ducts cleaned by an HVAC expert.

3. Thermal Expansion

Sounds from the ducts may not necessarily mean that there are animals inside. Sometimes metal ducts make loud banging sounds just because they're expanding and contracting with a change in temperatures. If this is the case in your home, you may need a contractor to come in and insulate the ducts.

Typically this type of noise occurs in cooler temperatures when your furnace starts running. The warm air causes the cold metal to expand, making a popping sound that's amplified into a banging or booming sound. If the ducts are square or rectangular (rather than round), this is more likely to happen. In addition, nearby wood framing means the noises are likely to be louder.

Insulating the ducts can help because the insulation absorbs some of the vibrations. You may need to place foam or rubber cushioning between the ducts and nearby wood too, and your HVAC technician may even be able to add duct liners to absorb vibrations from the inside as well.

These sources are three common reasons for strange or abnormal sounds coming from your HVAC system. Whether the noises are coming from your ducts or from your AC unit itself, Dick Kearsley Service Center can help you get to the bottom of it. Get in touch today to schedule an appointment with us.


520 S State, Clearfield, UT 84015

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Hours Of Operation:

Mon-Fri: 8:00 am - 5:00 pm

Saturday: 8:00 am - 4:00 pm

Sunday: Closed

Find Us On:


Davis/Morgan: 801-773-4836

Weber County: 801-393-1265

Brigham City: 435-553-4556

Salt Lake: 801-292-1636


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