Replies

1. 
   jet | Jun 26, 2007 06:06pm | #1

   It's called "oil canning". If you can isolate where it is happening than you can re-enforce the area with some straps screwed to it.

   "No doubt exists that all women are crazy; it's only a question of degree." - W.C. Fields
1. 
   ripmeister | Jun 26, 2007 07:02pm | #6

   Whys it called oil canning?  Squeezing the oil can and letting it pop back out?

1. 
   MikeHennessy | Jun 26, 2007 07:18pm | #7

   "Whys it called oil canning?"

   Old fashioned oil cans had their bottoms formed with a dome in the center so that they "popped" when you pressed on them to squeeze out oil.

   Mike HennessyPittsburgh, PA

2. 
   Brooks | Jun 26, 2007 06:06pm | #2

   The operation of the blower is going to create pressure differentials: higher than ambient on the supply side, and lower on the return side. A large span of sheet-metal in the ductwork can "bong" from flexing as the fan starts and/or when it shuts off. If you can figure what section is "bonging" and can get to it you can reinforce it with a small L-bracket to stop the flexing. If you can't get to it you'll have to live with it (as we do...)

1. 
   jet | Jun 26, 2007 06:07pm | #3

   Great minds think alike???
   Or Fools seldom differ?????"No doubt exists that all women are crazy; it's only a question of degree." - W.C. Fields

1. 
   Brooks | Jun 26, 2007 06:10pm | #4

   I liked yours better...

2. 
   ripmeister | Jun 26, 2007 07:01pm | #5

   Thanks Brooks.  I figured as much just wanted to make sure it wasn't some sort of performance issue.  Thanks again.

3. 
   MGMaxwell | Jun 26, 2007 10:38pm | #8

   Check your filter element and make sure it is not pulled "up" when the blower is on then falls back into place when the airhandler turns off. Usually the filter fits in a sheet metal channel. If for what ever reason the filter comes out of the channel it will flop up and down depending on the blower. 

4. 
   CapnMac | Jun 27, 2007 12:48am | #9

   Everybody hit the frirst two I thought of, filter element and oil-canning.

   One other item worth looking at is if you have a zone damper--those can develop an annoying habit of being noisy.  Sometimes, the damper, even ope, has just enough air resistance open to give the sheet metal a twist of bend--especially in the summer when the warm ducts are a tad longer and might be tighter in their joints than durign the winter.

   Hmm, if the filter is behind a central return air grille, check that it's in its clips, and not sitting on the grille.  Other wise, it lifts up whaile the blower runs to then settle on that grille with a stout 'bang.'

   Occupational hazard of my occupation not being around (sorry Bubba)