Just thought I would share, might help someone?

I own a 7500. Recently I replaced my 970 with an Onkyo 807 for pre/amp duties. In doing so I used the same 3 pair of Blue Jeans analog cables to power the 5 speakers. After 4 weeks in the set up I noticed a very audible hum (ground loop) going through all 5 speakers. I tried to diagnose with the amp in the system and couldn't get it to stop (checking all cables for solid connections, etc). I never figured it out so I pulled the amp from the system about a month ago and the hum went away.

Only last night did I get some time to play with it some more. To troubleshoot, I tested all of the channels of the 7500 using my Outlaw RR2150 as the preamp and everything worked great, so I decided to hook it back into the 807 fearing that I had a possible faulty pre/out on the Onkyo. As I was connecting all of the connections I figured out the problem even before testing it - the extra analog cable (3pair but only using 5 channels - 1 extra cable hanging loose). The unused cable had to have been crossing another connection somewhere causing the issue - so I split the pair and no longer have the extra cable back there.

One stray cable, simple fix, problem gone.