I know that the Auralex Gramma was developed to sit under a speaker/combo but has anyone tried to put it inbetween your cab and rack/amp. I had purchased one about 9 months to a year ago thinking it would help me out on those horrible stages we always run into at those hotel/wedding/corporate gigs. At one gig I was doing a sound check and I heard a rattling from my rack and thought "Oh no, not now". So I turned around and thought why dont I just isolate from the cab to the amp. It worked!? I have been doing this for a while now and it really got me thinking about how much vibration we give to our racks and bass amps over the 100's or maybe 1000's of hours we perform with our gear. I am sure it can't be a good thing.I can't even imagine what is going on iside a tube/hybrid amp. You probably wouldn't have to buy the Auralex like I did. You could cover some 3/8 or 1/2 plywood with carpet and get some foam from foambymail.com and be done with it for very cheap. I know it made a small annoying problem go away for me,and it made me feel alot better about what I was doing to my amp.