I'm having a similar issue with my new 7700. Prior to buying the 7700 I used five M200's with my 990 and there was no discernable noise or hum at any speaker at any volume setting. After installing the 7700 I heard 60 cycle hum that was easily heard 10 feet from the speaker. Interestingly the hum only appeared on the two surround channels and the center channel, the two mains were quiet - I'm not using the rear surrounds just yet. After rolling out my equipment rack to check my wiring again I noticed that the hum was reduced about 90% but still audible if you placed your ear close to the speaker which probably indicates some kind of wiring problem that was caused by moving the rack. I ran out of time to look into the problem further but will get back to it this weekend and report what, if anything, I find.

mike