Scary Furnace Sounds You Should Never Ignore

What’s that noise?! Is it banging, rapping, scraping, or screeching? Whether the sounds are soft or loud, it’s enough to give anyone the heebie-jeebies. You’ll want to investigate. It is the beginning of the dark, cold winter after all.

You let out a sigh of relief when you find out it’s just the furnace, but don’t breathe easy just yet. Those weird and scary furnace sounds can be much more dangerous than any supernatural force you were worried about.

From bangs and pops in the ductwork, to whistling and humming while the blower runs, most furnace noises are pretty harmless. But, there are some more serious noises to be aware of. Don’t ignore the following scary furnace sounds.

Loud Bang or Boom

If you hear a gunshot sound go off when you turn on your furnace, you may have a gas build-up in the system. Never ignore this loud sound coming from the furnace. It could crack the heat exchanger, which is both dangerous and expensive. Turn the system off immediately and call a professional.

Dirty burners may have delayed the ignition, which causes gas to build up and “explode” when the ignition finally comes on. Annual fall furnace maintenance will take care of this problem since your technician will inspect and clean the burners as part of the tune-up.

Expanding and contracting ducts could have caused the loud bang or boom, but this sound is normally easily distinguished from a gas build-up “explosion.” It’s a common problem that homeowners with central HVAC systems have to deal with. Luckily, there are ways to prevent loud duct noises. Contact a professional HVAC technician to take a look. Solutions may include sealing and insulating ducts, replacing undersized ducts, adjusting dampers, or replacing the air filter.

Metal Against Metal

If you hear loud clanking and scraping, you could have a serious problem with your furnace’s blower wheel. Turn off your furnace immediately and wait until a professional HVAC technician has had a chance to inspect the system

  • The blower fan may have come loose and is now hitting the blower house casing. If the blower wheel/fan isn’t too damaged, the repair should be quick and easy.
  • The blower fan may be broken and need professional replacement.
  • If the piece holding the motor and blower assembly together has broken, the whole assembly may have dropped and is now hitting the housing. A professional diagnosis is needed.


A rattling sound coming from the furnace can indicate a loose panel or a loose screw. Before attempting to work on your furnace, make sure you turn off the power at the source. Then, you can try tightening your panel with a screwdriver to see if that fixes the rattling sound.

If it’s not a loose screw, it could indicate a leak or crack in your heat exchanger, which can be very serious. Faulty heat exchanger can leak dangerous (and potentially lethal) carbon monoxide into the home. Contact your local HVAC company right away if you cannot solve the rattling sound by tightening a screw or two.


There’s a difference between rattling, banging, and rumbling. A rumble sound normally indicates a furnace that hasn’t been maintained in a while. This usually means dirty gas burners or a pilot light that needs to be adjusted.

The furnace flame should be blue, which indicates a clean and efficient burn. It’s fine if there is a small yellow tip, but if your flame is any other color than blue, contact your HVAC company right away. A lot of red, yellow, orange, purple, or green indicates inefficient and potentially hazardous conditions.

High-Pitched Squealing or Screeching

The fastest and most effective way to fix this problem is by calling your local HVAC professional to take a look and fix the problem for you.

If, however, you would like to find out what is going on and see if it’s something you want to handle, continue reading.

Squealing, whining, and whistling noises aren’t as big of a deal as metal-against-metal and booming noises, but it’s still something you want to keep an ear out for.

  • If you have a belt-driven motor, loose, or damaged blower belts can cause a squealing or similar sound.
  • Shaft bearings and other moving parts may have become dry. Contact a professional technician to lubricate your moving furnace parts. Again, a fall furnace tune-up would have taken care of this issue.
  • Malfunctioning blower motors may be the culprit. Contact a professional for information on repair or replacement.

We hope your Halloween is scary, but safe. If scary furnace sounds are keeping you up at night, schedule furnace repair from one of our brave Service Champions.

As you might expect, you can avoid most of these frightening furnace noises when you remember to schedule fall furnace maintenance with a qualified professional. Better yet, sign up for a home maintenance plan to get these annual HVAC tune-ups scheduled for you.

In order to prevent carbon monoxide leaks and the scary hallucinations that come with CO poisoning, it’s important to schedule annual furnace and fireplace maintenance before the heating season starts.

Additionally, make sure you have working CO detectors on every level of the home and outside of each sleeping area. Remember to test both your CO detectors and smoke alarms every 30 days. Replace them at least every 10 years (or sooner, depending on the manufacturer instructions).

Service Champions is known for trustworthy, on-time home service throughout the East Bay, South Bay, and Sacramento areas. Contact us today for our tune-up special!

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