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.
Maybe cross breaking wasn’t enough and the are to help keep the expansion/contaction noise down. Never seen them before really…
Larry’s got it.
It damps out the duct pop on blower start up and shut down.
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. 
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?
Is that cheaper than dyna mat?