Duct Noise

[Ben Chou]

Please link to Duct Noise: 20120121-003623H.wmv - YouTube (http://www.youtube.com/watch?v=LRri3uz1Twk)

Date & Time 2012/01/21 - 00:36 AM
Outdoor temp: 3 degree C
Inner temp: 20 degree C
I heard the noise and recorded it when heating is on about 2 minutes later, but there is no noise at 5:40 - 9:50 from the scroll bar when heating is off that it may be at 7:40, and the noise appear again after 9:50.
Can anybody tell me what cause this kind of noise?

Thank you.

[Jim Luttrall]

My guess would be metal duct work bound-up and rubbing on wood framing, etc. when the heat is on and metal is expanding then again when the heat cycles off. Just a guess though since I did not take the time to listen to the entire recording and I was not there. Call a good HVAC guy experienced in metal duct work and be prepared to tear out some sheet rock to access the problem... or just live with it.

[Joseph Hagarty]

i would think thermal expansion and contraction
but the recording suggests the noise occurs every 10 - 12 seconds
i have no idea.....