Rattle, Buzz, Clang: The Sounds You Don’t Want Your Furnace To Make

  Posted on May 22, 2017

Different brands and types of furnaces make their own, unique noises, but some sounds serve as universal warnings that problems may be brewing. Knowing what to listen for could be the very thing that prevents costly repairs and time spent bearing subzero temperatures without a working heater.

Anytime your furnace starts making a rattling, buzzing or popping sound, something could be wrong. Before a part breaks, it usually starts making noise. If you just ignore it, a part that could have been salvaged may break beyond repair, at which point you’ll spend more money to fix the problem.


If your furnace makes a buzzing noise, you may have a transformer issue.  The box may not be mounted securely (this is a common problem), or less likely, the transformer may be on its last leg.  You'll also hear buzzing is your blower motor is failing.  That's the motor that powers the fan, and it can buzz (or sometimes hum) in its death throws.

Boom! Thud!

The ducts could be making this noise as their metal bodies expand or contract, which is natural.  Probably best to call a professional if it's not the ducts because it could be an issue with your gas valve.


First, check your bearings and motor mounts. Chirping can be cause by loose mounts. If you hear it just as the machine kicks on, it may just be a natural noise the fans makes as it starts up.


If you hear a metallic clang, it's most likely your ducts—not your furnace.


You might have a loose, broken, or cracked belt.


Sometimes furnaces rattle as the metal inside begins to cool down.  If the rattling become noisier than normal, call a pro.  It may be a motor bearing to blame if it only happens when the furnace first starts up. This, also, might be a cracked fan belt.


Usually the culprit behind noisy and abrupt screeches is your blower motor.  It could be the entire motor or just a bearing.

What’s Normal?

Not all sounds are something to be concerned about. Normal noises include a low, light hum created by the furnace’s inducer motors, air noises coming from heating registers, and a clicking noise as your heater’s gas valves open. A click-click sound is also normal as your thermostat kicks on.

When in doubt, the safest bet is to turn to an experienced professional. And when you do, ask about trip fees. At BERS, we don't charge homeowners a fee to investigate a possible problem. Our philosophy is that if we don’t do any work, there shouldn’t be a bill. While the workload of the contractor is an important contributing factor, for most problems same-day service is a realistic expectation.