What is this on the Ductwork?

[Ian A. Niquette]

Does anyone have any idea what these black stickers are on the ductwork? They felt slightly tacky to the touch. I thought they may have been covering holes, but they were not. They were on all of the ductwork, and I have never seen this before. Any ideas would be appreciated. Thanks in advance.

[Larry D. Kage]

Maybe cross breaking wasn't enough and the are to help keep the expansion/contaction noise down. Never seen them before really...

[Michael Larson]

Larry's got it.

It damps out the duct pop on blower start up and shut down.

http://www.acousticalsurfaces.com/hv..._vmax.htm?d=26

[Marcel R. Cyr]

Never seen it either, but that is what came to mind first too.

Possibly a thinner sheetmetal than normally used and the duct was drumming with the velocity of the air.

[Ian A. Niquette]

Thanks guys. Interesting, I had never seen this set up before. Looks like a good product. Mike, how do you always seem to come up with the magic google location?

[Bruce M. Graham, III]

Is that cheaper than dyna mat?