thump sund in heating duct

there is a banging noise in heating duct shortly after furnace comes on it only happens once. Is this due to the expansion of the sheet metal?
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Either that, or Bruce Willis is filming another Die Hard movie.
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t&k wrote:

When the fan goes on the pressure in the ducts change and some of them may flex in or out. You may notice that larger panels are often creased to provide a little more strength to prevent this problem. If you hunt down the specific part that is flexing you may be able to shim or stiffen it to eliminate the sound.
--
Joseph Meehan

26 + 6 = 1 It's Irish Math
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an alien chasing sigorney?

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Yes, it's called the "oil can" effect. Just a nuisance, nothing more...
Ed
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On 30 Dec 2004 04:33:18 GMT, snipped-for-privacy@aol.com (AUSTIN1880) wrote:

Actually, its called, "The ductwork probably isnt sized properly". Most likely, the furnace is too big or the ductwork is too small. Either way, it means a shorter life span for your heat exchanger and associated temperature controls in your furnace like the high limit. Then of course we can get into the air conditioning but thats a whole nother story. Bubba
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Sounds like a demon. Better call TAPS. Joe
t&k wrote:

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I watched that show last night.... finally was forced to turn the channel when I saw em flashing that $10 temp probe around and being astounded when it went from 60 to 50 to 45 to 60..... Well, um.... DUH.
The every 15 minute adverts for roto rooter don't do much for me either.
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Yes, it's called the "oil can" effect. Nothing to be concerned about, merely a nuisance...
Ed
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