Originally Posted by rritterson
So, if you pick up and move speakers, but leave the wires, the new speaker at the same wire location will hum. But if you leave the speakers and switch the wires at the receiver, the hum disappears?
Essentially, then, the interference only occurs if a wire is connecting one particular receiver connector and one particular physical location?
That makes no sense as a ground loop issue even if you look past the "only on one output" question, unless the ground loop is caused by the location of the speaker somehow.
Is it possible you have mounted the speaker to a conductor, either a pipe or wire run or metal stud and it's now conducting power from either the coax or power strip through the speaker transducer and wall? Most speaker housings are not conductive, I know. (Also, this answer doesn't explain why the hum doesn't jump receiver outputs to whatever speaker is at that location unless you also have an AVR fault)
Do you have an oscilloscope? You could monitor signal from each AVR output and confirm it still happens even when no speaker is plugged into the humming output and/or confirm it's really 60hz and a ground/power issue and not some other interference.
Sounds like a possible compromised speaker wire? like it has a staple through it or a nail, drywall screw, etc... somewhere along it's length?
If possible do a temp run of wire straight from the offending channel to the speaker. Sometimes installers staple the wires in and compromise the insulation jacket on the speaker wire, or heaven forbid the electrical cable in the wall. I doubt the OP's power runs are damaged since that is typically checked on inspection during cunstruction, but the low voltage cables like speaker wire, phone, Ethernet and coax can get overlooked and are very easy to effectively break by damaging the jacket.
I also work in IT plus do installs sometimes and this doesn't sound like a ground loop from the potential difference between the CATV live to the TV because running the coax through a power strip did seem to affect it but it could be the HDMI back-feeding somehow, I just never hear that happen to a single channel on a amp.
The OP could test the ground on the tv with a cheater plug if it is a 3 prong power cord but after a point disconnecting grounds get dangerous for either your equipment or yourself if somehow a components chassis gets energized so I don't recommend disconnecting the CATV ground over getting a pro over with test equipment to take a look.Edited by undermined - 4/9/13 at 3:12pm