I just double checked the connections at the plasma;

Nothing plugged into the plasma and plugged into the wall = no buzz
Only the 1 HDMI cable plugged into the plasma w/o it plugged into the wall = no buzz
Plug the plasma into the wall w/o turning the plasma on = buzz

This was done with everything else plugged into the Marantz 7005 (4 HDMI in, 1 out, plus 2 optical cables, and 8 RCA cables from my Oppo into the 7.1 input).

Suggestions?
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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.