While some noises are normal, such as a quiet hum or the sounds of air whooshing through the vents, sometimes HVAC systems make strange noises and can become loud, disruptive annoyances in the home. This doesn't have to be the case.
Check out these common causes of noises in an HVAC system and what you can do about them:
Hearing a rattling noise coming from your HVAC system could mean a few things. If it originates from the outdoor unit, chances are you have some kind of debris in the system, such as a twig. (While the grate will protect your system from most large debris, it's still possible for small things to get through.)
Turn your system off and cut the power to the unit, then remove the debris. If you see visible damage to the condenser coils, compressor, or fan, call your HVAC technician.
If the rattling seems to be internal, from a furnace or other internal component, turn the system off and call your HVAC technician since removing the obstacle isn't as simple.
Hearing a hissing noise most likely means air is escaping from your system. If the noise is coming from the walls, there's a good chance your ducts are leaking. Not only can this cause noise, it also wastes money because the air that should be circulating throughout your home is leaking into the walls.
Duct repair isn't really a repair homeowners can do on their own, so if your system is making a loud hissing noise, call a technician. However, if the hissing is light, it could originate from your air vents. Typically when you hear this noise it is because your filter is not “set” right or you have the wrong size filter which is creating the gap in the seal. If this is the case, the air is squeezing past the filter or around it, instead of being pulled through it. This is a simple fix that starts with ensuring the filter is the right size and is placed correctly, leaving no room for gaps.
An HVAC system that is running normally will make a humming noise. But if it's clanking, that's a sign that something is wrong. It could be loose parts, such as the blower motor fan, loose blades, or loose pipes that are rubbing together.
Clanking noises are a bit more serious because loose parts, if not addressed, can cause costly damage to your system. Your best bet is to turn the system off and call your technician.
Keep in mind that your HVAC system is exactly that — a system. As it works, it will make noise. Hearing the motor running or humming, as wells as the fans blowing or air moving through the vents, is totally normal. However, unnatural sounds like rattling, hissing or clanking, or the sounds becoming loud enough to be disruptive, can be signs of problems.
As with anything else, regular maintenance tune-ups, changing air filters, and other general repairs are the best way to avoid this, as well as knowing what sounds are normal and which ones are cause for concern.