[Smashy]

I moved into a new home recently, and the knocking sounds made by the ductwork when the furnace runs are so loud that they wake me up. I wouldn't mind light knocking noises but this sounds like somebody is banging pots and pans right next to my bed. The knocking only happens while the air blows. There is one loud knock approximately every 10-20 seconds.

The funny thing is, the knocking only occurs at night. Right now it's day time, the furnace is blowing air, and there is no knocking. I believe it might have something to do with the fact that I keep the temp at 70 during the day but only 62 over night (I like it cold when I sleep), so the metal ductwork does more contracting and expanding during the night than during the day. Anyways my question is, how can I eliminate or at least reduce these loud knocks so I can get a good night's sleep?

 

[Ron6519]

Are the exposed ducts insulated?

 

[sktn77a]

Thermal expansion. You could try sealing the ducts with Tape and Mastic but that may not eliminate the problem. Are the ducts un-insulated and in and un-conditioned space (attic, crawlspace)?

 

[Smashy]

My bedroom is over the basement. I went down to the basement and snapped this picture of the duct going to my room. I am not 100% sure this is the duct making the noise, but other nearby ducts all look pretty much the same.

 

[Windows on Wash]

That outside duct is getting super cold because of a poorly sealed and insulated rim joist.

When it gets that cold, it's going to be super noisy as it grows.

Look in the insulation forum for ideas on how to insulate and seal the rims.

 

[beenthere]

Post a pic of the duct that supply comes from.

 

[Ron6519]

In my limited experience, the ducts that I've seen/heard that makes the noises are the large supply and return ducts. Not so much the individual room supply ducts.
What you need to do is identify the ducts making the noise. Or, just insulate all the ducts as they should have been at installation.

 

[Smashy]

Unfortunately the large supply/return duct is covered by drywall (the previous owner had partially finished the basement) and I don't really feel like tearing up the wall. I guess I will just have to put up with the knocking, during the winter at least.