Hi there! thought i should add this..
My 7000 remote has only JUST started making the buzzing noise (just as you describe) & only when the backlight is on, i have had it for 5 years since it was purchased from B&O completely refurbished (including the remote). the only difference is i have shipped it from Australia to Switzerland (professionally packed for shipping container) and plugged it in here in Switzerland (same voltage here as in Australia - as i understand).
it was in a quiet room in Australia, and as well here in Switzerland so im sure its a new sound.
Sorry to throw this thread up on its head but thought you might all like to know.
its a little dissapointing as its nice to have the room completely quiet to exprience the lovely clarity of a B&O, regardless i still loyally love this system - even with the annoying buzz.
regards, Chris