I'm using a PSW505 subwoofer and I recently got a new Denon AVR790 receiver and all of a sudden I have some low frequency hum coming from my subwoofer when the receiver is off and the subwoofer is in the auto state (so it doesn't go to sleep after 15 minutes). My old receiver was an Onkyo RT-530 (from a HTIB) and when I got the subwoofer I had the same sort of problem but moving the subwoofer cable away from the speaker cables seemed to help things and the hum went away, but that fix doesn't work with this new denon receiver.
Just some other information...
If I turn the sub into standby mode there is no hum.
When I have the sub plugged into the wall without any cable running to the receiver there is no hum.
When I have the sub plugged into the receiver and the receiver is on there is no hum, but when I turn the receiver off the hum starts.
I do not have cable TV so there is no coax cable plugged into the TV.
I have tried multiple outlets and that changes nothing.
For the subwoofer cable I'm using a 25 foot Belkin Pure AV cable. Would having a short subwoofer cable eliminate the humming? or is the belkin pure AV cable pure cr*p?
I'm not sure if this is a ground loop or electromagnetic interference problem. but if anyone has advice/information it would be appreciated.