New to the TBX. Working with an unmodified unit. Thought I'd check with others for their experiences before digging into this issue. In addition to normal noise, I have a receiver that is heavily microphonic along with being deaf. Tubes test okay. Have a second unit I've exchanged tubes with no change. I see the second unit on hand has one of the 1N5 shock mounted. The unit which I'm working does not have that tube shock mounted so perhaps some microphonics is a normal condition for this chassis.