These toys are beginning to resemble a patch panel at the Bevatron - but with Gold-plated connectors. And $500 Or-more Speaker Cables [I'm not making that up, either.]

(I wonder who/what/where such a $Six Thousand box might be 'repaired'?)

As to the buzz - agreed, likely a missing ground - or 'added' ground loop!
"Walking in front of it" -- shades of RIAA phono inputs, and even, the plug in the wall at 'wrong' polarity. Bad PS filter caps == 120 Hz hum (not 60.. except with vacuum tube filaments). But a bad cap in other circuits: conceivably a buzz, I guess.

Offhand, I think a hardware kindaguy needs to assess this; doesn't usually translate well into a flow chart. Hell, it could even be some lo level amp picking up Tee Vee sync buzz! (often the case in the old days) Too many parallel possibilities. :-/


Luck,
moi