6 Different Noises Your HVAC System is Making and What They Mean

You might notice immediately when your HVAC system starts to make noises that are a little strange. Here are six of the most common sounds you might hear from your heating and cooling systems when there’s a problem, along with a summary of what it might mean.


While a buzzing noise coming from your HVAC system might seem innocent, it’s actually a sign that you may be having electrical trouble. If you hear buzzing coming from your AC or your furnace, it usually means that an electrical component, like a capacitor or a relay switch, is going bad.

The first step is to turn off your HVAC system to prevent it from burning out. The next step is to get a professional technician on site to perform a furnace or AC repair to fix the issue for good.


When you hear a rattling noise coming from your furnace, it’s likely that some part has come loose inside your appliance. While it could be as small as a screw, it could also be a more integral part. You should call a technician right away to get your furnace repair started.

For air conditioners, it could also be a small part. But because most units are outdoors, it could also be a twig or a rock. Getting an annual AC tune-up can help to prevent debris from causing problems.


In furnaces, a squeal usually indicates that a belt is wearing out or a part needs to be lubricated, two problems that are easily remedied by getting a furnace tune-up every fall.

However, if your AC is emitting a high-pitched shriek, it might mean that you have a refrigerant leak, which is a serious situation. While a technician may be able to repair the issue, the best option is usually a new AC installation.


No matter where you hear banging, it’s usually bad news. In an air conditioner, banging usually indicates a broken part, an unbalanced fan, or a dying compressor, all of which need to be repaired before the unit can be safely used.

For furnaces, banging often results from a build-up of natural gas. When it ignites, it makes a loud bang, and it can damage your furnace.


Metal on metal grinding is typically the result of bent or broken fans. This repeated contact can cause severe damage to the blades, as well as to the structure of your HVAC system. If you hear grinding, shut off your system immediately to prevent further damage. Then call a technician to take a look at the unit.


Soft whistling or a hissing noise usually points to a leak somewhere in your ductwork. While this isn’t as dire as some of the other noises, it does mean you’re losing much of the efficiency of your HVAC system into your walls, instead of your living spaces. An HVAC professional can seal your ducts permanently and correctly.

A Professional HVAC Contractor Near Me

When you need cooling or heating services, make T.E. Spall & Son your first call. Whether you need a furnace installation or an AC tune-up, be sure to CALL SPALL!

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