I just hooked up my 990 and 7700 today. The whole input configuration is a little tricky, as is trying to figure out how the remote works...

Anyway, I do not have any hum with the 7700 (using balanced cables), however when the amp shuts down, about 5 seconds later I get a whining noise in the right rear surround that lasts about 2-3 seconds. Its not loud, but it sure seems odd.
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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.