Thanks for the bad news.
I sort of figured that out after six hours of trying to eliminate the unrelenting HUM.
I do appreciate that someone else is going thru the same problem although I am not happy to hear you have a problem.
The strange part about it is that besides hearing it when all sources are off I really notice it when I engage my Pioneer Elite laser disc.
I disconnected everything, all power outlet cords except from both line conditioners (3500 3600) and component cables and the hum was still there.
So Einstien that I am, if everything is dissconnected and the only electronics that are plugged in is line conditioners and the HUM is still there, the HUM has got to be coming from the 3500 and the 3600.
So it looks as though I will be spending more money.
What are you going to do.