First off, I'd like to point out that I'm not on Todd's loaner program (I bought mine online from TTVJ.com). But since I'm often on the road, I also do sometimes hear the tube-inherent microresonance (slight pinging sound) mentioned here when I swiftly grab onto it, and I have to agree that the rubber on its volume knob does get easily snagged.
The pinging issue is not a biggie really (I seldom hear it), still, I thought of opening the amp and dampen its internals but that would surely void the warranty. So instead, I opted to wrap the whole chassis with 3M's double sided foam adhesive tapes and covered it with thick black leatherette. Furthermore, I changed the volume knob to a smoother version, and now it doesn't get snagged as much.
Here are some pics:
Now, unless the amp suddenly gets jolted, I don't hear the tube microresonance anymore even while on the move.
(I apologize if this seems OT, but i couldn't find a thread on this topic in the headamp forum to share this with)