Maybe totally unrelated but.........I discerned a buzz in my 402 mid/high left side UG Jube speaker. This was at idle "no signal". It is masked when almost any level of music is played. I will not say that I never noticed it before but I am fine tuning and trying to squeeze the best performance possible and it was easy to ignore in the past. I tracked it down to the in-wall wiring going to the left speaker. The electrician that ran the wires must have run some power wiring along side the speaker wire for too long a distance. When I swapped out the in-wall speaker wire with externally run wire the problem is gone.