8 Things That Can Cause Noisy AC and Heating Vents and How To Fix Them

Paige Bennett
Written by Paige Bennett
Updated August 12, 2021
Woman wearing headphones lying down on sofa
Innocenti / Cultura via Getty Images

Noisy air vents might be annoying, but they also could mean serious trouble

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Hearing a little bit of noise when your HVAC (heating, ventilation, and air conditioning) system is running is completely normal. But if you start to hear strange sounds, like rattling, clicking, squeaking, or grinding, it’s time to take a look. Here’s what causes noisy air vents and how to fix them.

Types of HVAC Noises

So how can you tell which noises are normal and which ones are the signs of a bigger problem? You should really only hear a low, blowing sound as the system moves cool or warm air through your vents. This noise shouldn’t be disruptive and will become more of a background noise as you lounge on the sofa or work at your desk.

The following noises coming from your ducts are more concerning:

  • Rattling

  • Clicking

  • Knocking

  • Banging

  • Hissing

  • Squeaking or screeching

  • Grinding

  • Buzzing

You’re probably pretty accustomed to the normal sound of your HVAC system, so if you hear something that sounds different from the usual, it’s probably time to call a local HVAC professional to take a look.

Causes of Noisy Air Vents

Exposed ventilation in a loft apartment
victor zastol'skiy - stock.adobe.com

Some of these issues, big and small, can be causing those strange sounds from your vents.

Closed or Blocked Vents

One common issue is that one or more of your AC and heating vents are closed or blocked. You may have left a piece of furniture pushed up against a vent after a thorough cleaning session, or, you might have intentionally closed vents in an unused room, thinking that you’re making it run more efficiently. However, both of these can actually cause the system to work improperly. This extra pressure can cause unexpected noises, so be sure your vents are all open and unobstructed to keep things quiet and running smoothly.

Old Air Filters

You should be changing your air filters every 90 days, but it’s easy to let this task fall by the wayside. Over time, dust and debris get trapped in your air filters. The filters will become less effective and can even become clogged if you aren’t regularly changing them.

You might also hear thumping, buzzing, or a high-pitched whistling sound due to dirty air filters. Try giving them a swap to see if the sound goes away.

Disjointed Ducts

If you hear rattling or clanking sounds, it could mean that your metal duct joints are loose or disconnected. Use metal tape to reconnect the joints, then call a local AC repair pro for a long-term fix.

Debris

Even with air filters, debris can still make its way into the ducts. This can cause rattling, buzzing, or flapping noises as the air moves the debris around the ducts. If you’ve replaced the air filter and still hear these noises, call a professional to clean the air ducts.

Leaking Refrigerant Line

A leaking refrigerant line will cause a hissing or bubbling noise as the refrigerant leaks. These noises are also related to valve leaks and compressor issues. Either way, these can be dangerous problems, so don’t try to handle this issue on your own. If you hear hissing or bubbling through the vents, turn off the HVAC system and consult a heating and cooling professional near you right away.

Electrical Control Problems

You might notice a “click” when your air kicks on or shuts off. This sound is normal. But constant clicking could mean issues with the electrical control through the thermostat. There could also be a system relay disruption. Replacing an old relay switch involves carefully handling wires on the old and new relays, but you can hire a professional to fix a relay switch for anywhere from $15 to $300.

Motor Issues

Several sounds can indicate potential problems with the HVAC system’s motor. Banging or rattling could mean loose motor parts, where humming could be a sign of a bad or unbalanced motor. High-pitched sounds, like squealing or screeching, might mean a worn belt or issues with the motor bearing.

AC motor repair costs about $300 to $600 to hire a professional. Attempting to fix an HVAC motor without the proper expertise could lead to further damage to the compressor and higher repairs costs.

Compressor

Compressor problems can have big consequences, so address them quickly. Hissing could indicate that compressor pressure is too high, while humming might mean a strained compressor. A failing compressor might also make a grinding noise. You have to have a license to handle refrigerants, so you’ll need to call a professional to repair the compressor. This will cost an average of $1,200.

How to Fix Noisy Air Vents

Noisy air vents aren’t just annoying—they can warn you that there’s a serious problem with your HVAC system. The longer you ignore the noises, the worse the problem becomes. That could mean a dangerous scenario or costly repairs down the line.

If you hear noises like whistling, it could be an issue you can resolve without professional help. Check that all your vents are open, and change your air filter if you haven’t in the last three months.

You can also remove vent covers and check ducts for small items that might have become trapped, like nails or toys. If you suspect disjointed ducts, you can remedy the issue with metal tape to reconnect the ducts and hold them in place, at least until you can hire a professional for a more permanent fix.

All other issues will require professional help. HVAC system noises could be a sign of major and risky problems that need skilled assistance.

HVAC Maintenance

To keep your HVAC system performing at its best—and quietest—there are a few things to keep in mind. Make sure you keep all vents clean and clear of debris and obstacles like furniture. Check vents after storms for leaks or signs of trouble. Avoid closing vents unless absolutely necessary to avoid putting additional pressure on the HVAC system. Don’t forget to replace those air filters, too.

Even with regular attention and maintenance, your HVAC system can end up causing noisy air vents. Take those sounds seriously, and call a professional to identify and solve the problem as soon as possible.

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