Why, there's a buzz in my NAD....

[natlus]

Not exactly a buzz, but more like a wooshing electric sound (herein referred to as the 'sound') that ebbs and flows with my NAD 7240 receiver. I'd like to try to fix it myself, and I'm trying to get the hang of this DIY thing...So some background:

1) I think I've isolated the sound as coming from within the receiver--I ran it through my cans, sans speakers, sans CD player, all unplugged. When a source is plugged in(ie, CD), it does not interfere with the music signal--the music sounds clear.

2) The sound does not change with the volume pot or bass/treble pots or the signal source switch.

3) The sound DOES seem to respond to the speaker switch--if I push or pull it a bit, the sound seems to back off, though it returns. It also changes sometimes when I turn the speaker switch back and forth from A to B, etc..

4) I've used DeOxit power booster and Gold Connector on as much of the speaker switch box and switch behind the face plate, as well as blew out dust, cleaned other pots, etc..Anything I might have missed or a particular connection I need to attend to?

5) I've tried another outlet with same results. The current outlet is used with a Monster Cable AV200 Surge protector. Finally, when I turn the receiver off, the sound builds up and dissipates.

Thanks in advance!