My 7700 makes almost a whirling noise when it first turns on, but then it gradually goes down. It is audible, but only if you are right next to it.

I also had a ground loop, but was able to determine it was caused by having a digital coaxial audio cable plugge din. I am only using opticals now, and it sounds great. If I put my ear right next to the speaker, I can hear a faint noise coming it.
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Panasonic TC-P65S1 65" Plasma HDTV, Marantz AV 8801 Preamp, Outlaw 7700 Amp, Klipsch RF7 (X-over dean G modded) RC7 (X-over Dean G modded) RS7 CDT-5800C speakers, Outlaw LFM1 EX Subwoofer, Oppo BDP-93, B & O Turntable, Toshiba HD-A2, Sony CD & DVD 400 disc jukeboxes, DirecTV HD-DVR, PS2, PS3, Wii, Harmony one remote, Monster PowerBar 1200 for the TV, sub, PS3, HD DVD and Wii, Tripp Lite Isolation Bar for the Amp, Pre-Amp and other sources.