Audio Feedback with Multi Zone Output

[HDefinicktion]

So, here is my problem.  I have my Denon in the theater hooked up as usual, and I changed out my secondary receiver that powers four zones in the house.  I connect the Denon to that receiver through the Multi Zone RCA output in the back.  Nothing else has changed with wiring.  I moved the receiver that I used for to power the four zones to the living room to power that surround sound system.  The sound is fine from the four zones from the output from the Denon, but the speakers hooked up to the Denon in the theater hum when that cable is hooked to anything.  I have tried a straight cable instead of the one in the wall, but same thing.  It works fine if the only thing plugged into the Multi room receiver is the RCA audio cable from the Denon.  As soon as I plug something else in, the main speakers begin to hum.  Anyone have any ideas as to what it might be...

Nick

[HDefinicktion]

So, I think I have found the issue...a ground loop.  Has anyone entered into this realm before, and if so, what solutions have you used?  I have seen ground loop isolators range in price from just around 10 bucks to around 200 bucks.  Any insight would be appreciated.