Thanks for the link, Troy! But your link shows a one-inch foam; I think that "speaker construction" stuff blocks too much airflow, and that the right product to use is the more-expensive-per-square-foot but MUCH thinner Cascade Audio "sheet" product,
http://www.partsexpress.com/pe/showd...number=268-260 The VB-2HD stuff, at twice thickness, would do a significantly better job of damping, but it's not available for sale in the "MiniPack" sheet size, so it would cost almost 3x as much to buy.
I'm gonna line both the aluminum output "plate" and the vertical output tubing which blasts onto the plate, there's probably a lot of vibration there too. Like you, I "upgraded" the input filters too. (For filtering more dirt, not just for noise). Here's my post about that:
http://www.trailmanorowners.com/foru...0000#post40000
It seems awfully sloppy that the vertical tube blasts down onto a
completely horizontal plate, without even the slightest bit of angle to direct the airflow towards the (louvered) front and rear register vents. I might slap on some shim-like stuff, underneath the noise absorption pad, to help direct the flow a bit. I guess that this improvement will more than make-up for the slight decrease in diameter which the noise-absorption sheet material will create.
For the horizontal plate (not the veritical tube), I might use two layers of the VB-2 "thin" stuff, at least for the center area (directly beneath the vertical output tube, more or less). I'll post my results after the "upgrade".