1 ruger9 2 weeks ago Supro Tremoverb. It didn't rattle when I got it, but after I swapped some tubes, the rattle began. [but it's not a tube... read on...] It's for sure rattle from the upper back panel- because when I remove that back panel, zero rattles. I tried tightening the screws, loosening the screws, and also putting very thin foam between the panel and the chassis (note: not between the panel and cabinet... more on that in a second), all to no avail. "Rattle" may not be the best word... it's a "resonance" I guess... but the term "cab rattle" is the commonly used phrase.That panel is friggin butt-tight. When I tighten the screws down that hold it on (all the screws go into the CHASSIS, not into the cabinet like on fender amps), the panel actually makes noise as I tighten it down because it's such a tight fit; I think the panel is actually bending a little as I tighten the the screws. When I loosen the screws, you can see the panel moving back into place a bit, when the tension is removed.I tried putting very thin foam between the panel and the chassis, and that didn't work either.So, I've googled, I've already tried everything I can think of. Any help? The rattle is driving me insane, and it really p's me off because it wasn't there when I brought the amp home... it's like something has changed in the relationship of the back panel and it's mounting to the chassis. Also, just to be more clear: it's not that tube cage, or the tubes. When I play the amp as pictured- no back panel- ZERO rattles.it seems to be happening where the tolex of the panel touches the tolex of the cab; as I said- it's a VERY tight fit.