I use a single rubber damper (the 10-cent variety) on the driver tubes on my M-125s. The front tubes tend to be very sensitive to harmonics and the damps have helped. Tried 'em on the phono and line preamps but heard no difference, so those tubes are nekkid.
I had a horrible subsonic rumble feedback through the system with my VPI Traveler turntable. Took Dick Vandersteen's advice and mounted a wall-shelf for the turntable, the theory being the floor and the wall have different harmonic frequencies.
That, and some tennis balls under the Traveler took care of most of the problem.
However, there's an even more elegant solution and that's one of Kevin's (KABUSA.com) RF-1 rumble filters here:
http://www.kabusa.com/rf1.htm for about $100. It's an active subsonic filter and cured all ills. Goes in the line between the phono preamp and the line preamp. It cured all my turntable ills. Before engaging in serious carpentry, I'd try one of these. It's about the size of a pack of long cigarettes. Kevin is a hoot to talk to as well and if you're an Ortofon cart freak has great advice (and prices) on those as well. His website sucks, so it's just best to call.
I put cheap Sorbothane feet under all components, amps and preamps. Can't see the need to go the mag-lev route, no matter how attractive they are to polar and bi-polar personalities.
I remember when the first Hafler solid-state amp (DH-200?) came out, and built one. It had a terrible hum, physically as well as through the speaks. Asked around (pre-internet days) and found this was a common problem, and the solution was to put a brick on top of the cabinet. That worked!
Sometimes Occam's Razor applies to audio, too.
Last edited by deepee99 on Thu Apr 03, 2014 3:51 pm; edited 1 time in total (Reason for editing : Clarity, if such exists)