I have an Ampeg Jet (15 watts 112) combo, and attempted to fix some rattling, but it seems that power tube rattle is just here to stay. I used 2mm rubber tape with glue on one side (normally used to insulate pipes) to insulate most of the chassis, ruling that out as a possible source. Then I added some to the metal bar that holds the power tubes, then I made a 3-sided cardboard cage for the tubes and insulated that, and wrapped it around the tubes with rubberbands (leaving room for air to move). The power tube rattle refuses to go away It's a shame because I love to crank this thing. Of course, this probably wouldn't show up on a recording if you mic it from the front, or in live situations with a drummer, but it's annoying when jamming alone. So, FYI, rubber tape insulation doesn't dampen power tube shimmy.