I've been fortunate with mine that it doesn't buzz but I bought some interesting stuff at a craft store (yes... I said craft store). Creatology Fun Foam. Comes in nice big 12x18in sheets, is 1/16in thick, you can get almost any color, it is nice density foam and can be cut to any shape you need. Oh yeah... it was cheap too. I used it to make custom foam washers for my window install and also to isolate a fan that was bugging me on another computer.
"Computer supplies" at a craft store... who knew! Link
EDIT: I think I'll make a thread for this in the Case Mods General forum and see what happens hahahaEdited by HAFenvy - 10/7/09 at 11:48am