This has been reported before and I do recall participating in the discussion, but I subsequently forgot. After a recent move, my mains voltage is no longer ideal; depending on how many air conditioners are running in the area, it can sag down to and below 112 VAC.
The BeePre does not like this. From tests with a variac, my mains is on the razor edge and below about 113V my right channel throws a fit and emits a loud, obtrusive buzz.
Fortunately my variac can go over line voltage and has a built in meter, so it's now semi permanently installed feeding the BeePre. Slight adjustment to 120V and back to whisper quiet. There's a definite sharp threshold where this happens, it's not gradual.
Thought it was worth posting this again since I couldn't find the old thread, and it really should be one of the standard troubleshooting steps. For some reason my BeePre's right channel throws a fit first, and it doesn't follow a tube, so it mimics other issues where you'd usually be looking for a cold joint or similar.
