So in step 2 above the buzz starts when an hdmi cable is plugged in only one end with the other end unplugged? Did you try a differnt hdmi cable in that condition? If the tv hdmi cable is somehow the problem it could affect all your othe tests. You should not have any noise using the RCA cables. At this point I think it is a problem with the tv or a cable but that doesnt jive with the RCA cable noise.
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Music system
Model 990/7500/Magnepan 1.6 QRs/Technics SL1200 MK2/Aperion S-12 Subwoofer/OWA3/Sony NS75H DVD
APC H15 Power Conditioner

TV System
Large Advent Loudspeakers/ Polk center/Monoprice surrounds/Panasonic Viera 42 inch/Onkyo HT-RC260/Sony BDP S590/Directv


Home Theater System
Onkyo PR-SC886/Outlaw 7125 Klipsch RF-82 L/R,RC-62 center, RB-35 SR/SL, BENQ HT1075, Outlaw LFM1-EX/OPPO BDP-83/Directv
Harmony ONE
Blue Jeans and Monoprice interconnects
APC H15 Power Conditioner