Most likely the blower fan has become loose and is creating the sound by hitting against the blower house casing.
Furnace blower wheel noise.
Check the set screw to ensure that it is properly tightened.
The blower cabinet in most older furnaces is essentially a hollow tin box with a motor and fan hanging from the top.
Thumping and vibrating sounds are the results of an unbalanced blower wheel.
The blower wheel is attached to the blower motor shaft with a set screw.
The wheel may have become loose and is making the noise by hitting the blower casing.
A broken motor mount causes the blower wheel to drop and rattle against the housing.
Sometimes a broken blower wheel can also be the source of this distinct noise.
Having one of our techs tighten the blower wheel can often resolve this problem.
A few blower wheel problems include.
Get a professional to tighten the wheel.
If you hear this sound turn off your furnace immediately.
Here are some of the reasons your furnace could be making a funny noise.
Moreover the motor mount.
The blower wheel is broken and.
When your furnace blower wheel is broken it will make your furnace sound like metal scraping against metal and will really hurt your ears.
The cause of this noise is usually a problem the furnace s squirrel cage blower wheel.
If the set screw is loose the blower wheel will wobble on the motor shaft and the wheel will be noisy as it turns.
Blower wheel is loose from the motor wheel.
Shut your furnace off if you have a compromised mount.
How to reduce heating cabinet noise.
My furnace which is 13 years old has 3 8 acoustic soundproofing inside the blower cabinet with a cut out for incoming air.
If you hear this noise turn off your furnace immediately to prevent any further damage to the furnace.
The blower wheel blows air out of the furnace and through the house.