@branch300bpm I would guess that a ground loop would be always audible, not only during bus activity?
@root42 no, this depends on electrical activity on either side. Since Commodore drives are self-contained, when they are idle they don't do much electrical interference that could pass on to your speakers through your machine.
@branch300bpm hm, I can beep out all the pins and shielding of the IEC port, I guess.