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Old 03-21-2013, 05:02 PM   #1
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Noisy from cold air return


A few months ago a contractor was leveling some floor joists to prep for Hardwood installation. Ever since, when the furnace is running, there has been a hum coming from the cold air return closest to where the work was done. The furnace maintenance guy said it was not the fan motor. Any ideas anyone?

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Old 03-21-2013, 06:03 PM   #2
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Noisy from cold air return


Something left on top of a duct? Like tools or construction debris?

Is it a machine-like hum or a buzz like from electricity? If it's a machine hum then I'd bet on there being crap on the duct. But if it's a buzzing noise then you'd better break out your voltmeter and make sure the ductwork hasn't been energized with live electricity.


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Old 03-21-2013, 06:57 PM   #3
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Noisy from cold air return


It's a hum. I was also thinking that something was left on top of the duct. Guess I'll have to break out the flashlight!
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Old 03-21-2013, 09:10 PM   #4
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Noisy from cold air return


If the hum goes away when you place both hands flat against the return air grill, you have a harmonic vibration.
Let us know.
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Old 03-23-2013, 06:40 AM   #5
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Noisy from cold air return


Noise went away when I placed both hands over the return grill. So how do I fix it? Thanks
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Old 03-23-2013, 06:44 AM   #6
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Noisy from cold air return


Over, as in completely blocking the air flow? Or, as in pressing against the frame of the register to help prevent vibration? If it's the latter then it could be as simple as improving how the register is mounted to the duct. If that's the source of the noise. Try removing the register cover (the grille) and see if the noise goes away. If the noise goes away then find a way to better secure the grille so it doesn't rattle.

But if the noise continues after the grille is removed then it's the how the duct is secured inside the wall.
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Old 03-23-2013, 03:58 PM   #7
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Noisy from cold air return


If you have a metal return air grill you can
bend every second slat 20 degrees from where they now are with needle nose pliers.
or replace the metal grill with a wooden grill.

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