My Furnace is Making Funny Noises. What do I do?

By admin,

“Ka-clunk, ka-clunk, ka-clunk.” It’s making that sound again. Your furnace recently became musical, and the random symphonies don’t seem to be going away anytime soon. Some noises are a normal part of the operation of your furnace. How do you know if you need furnace repair?

The Loud Start: Pops and Bangs

Pops and bangs are not uncommon for systems utilizing sheet metal ductwork. When your furnace kicks on and the fan starts, it is pulling air through the ductwork. This causes negative pressure that can make the sheet metal constrict or suck in. On the contrary, when the fan stops the ductwork is allowed to return to its normal state, causing the sheet metal to expand. Minor popping is normal, but a loud pop could mean your ductwork is undersized, poorly braced, or that your filter is clogged. You will want to get these issues fixed, as they can lead to low energy efficiency and/or leaking, dropping dust into your home. Popping could also simply mean that your vents are closed.

If the pop is especially loud, closer to a bang, and accompanied by zero hot air, you should be concerned. In this case, your furnace burners are probably dirty and allowing gas to accumulate in the furnace before it ignites. The bang is caused by all of that gas igniting at once. Be sure to get your furnace checked immediately. This is dangerous as it can cause a crack in the furnace heat exchanger, containing gases dangerous to breathe.


There are a few reasons why your furnace might be humming. First, it could just be a loud transformer. This is nothing to worry over. However, if your fan motor hasn’t been receiving the maintenance that it needs and has become overworked, you could have a failing motor on your hands that needs help before it kicks the bucket. Alternatively, your starting capacitor may be ready to die. Either way, you should get your furnace checked.

Rumbling or Growling

Rumbling or growling associated with the start of your furnace could also indicate a problem with dirty burners requiring cleaning, or the pilot light may need to be adjusted.

Rattling, Thumping, Clanking, Banging

Any of these sounds could indicate that the blower wheel is out of balance. This is not an immediate concern, but it could create bigger problems for you later by hurting other parts of the system. Rattling in particular often indicates loose components such as the motor mounts or bearings. Your furnace should be repaired before these parts break or disconnect. If rattling is followed by a loud banging, you should shut your system down, something has broken or disconnected.

Schreeeechs, Screams, and Squeals

If you are hearing a painful, metal-on-metal, nails-on-a-chalkboard type screech, the blower wheel may be loosened from the motor shaft or broken off, hitting the housing as it rotates. Shut everything down. This can cause permanent damage to your blower housing. The schreeches could also be caused by a broken motor mount, motor bearing problems, or a bad belt. The motor mount may need to be fixed, the bearings may need oil, or the belts may need to be replaced.

Whap, Whap

Imagine the sound a bike wheel makes when playing cards have been attached to the spokes. This is what it sounds like when something is stuck among the blower blades or within the housing, making contact with the blower as it turns. Whatever is causing this sound should be removed.


A clicking sound is normal for when your furnace is turning on and off, however, repeated clicking sounds can indicate a problem with the ignition system, where the igniter is failing to ignite the pilot light. This should be checked.

Whatever the sound may be, it is important that you don’t attempt furnace repair on your own. Furnaces are electrically wired and contain dangerous fumes. If you are experiencing a concerning noise, contact your local heating service representative.