Originally Posted by sawfish
Given that plasmas hum on light colored images, and it can be tricky to isolate the source of a noise, I would verify the hum disappears when I disconnect the speaker wires, or at least verify it tracks the receiver volume level.
What kind of UPS? The common ones pass through wall power when they're not operating from battery, and it's only when operating from battery that they output stepped-sine wave.
Simplifying the system and adding things back is all I know to do, but I would definitely first verify it is indeed coming from the speakers. In fact, I'd pray that I was fooling myself, and it's the TV doing the ordinary plasma buzz. That said, if you're getting pixelation from the cable box, that would be the thing to start with.
Thanks for the replies.
I will check the cable dressing in the morning: I thought I had everything pretty well run, but we have cats, and who knows what may go on back there.
I'm trying to study up on ground loops, isolation transformers, and such (this is a 1930's house, wired who knows how, with a 1970's addition, basically two wiring systems), and it seems to me that perhaps I should be running the whole system from one receptacle (I had them spread around since 2000W+ seems like a lot for one power outlet).
I am considering, after removing all antennae, IR remote sensors, and peripherals except for the (swapped) cable box and dressing the cables rigorously, going from Mains > Monoprice Power Conditioner > three CyberPower CST1300AL UPS's, with the Denon and Panasonic each on their own UPS. If that neither explodes the house nor fixes the issue, I will look into Isolation Transformers. Might work, might not, but I am not aware of an electrician in the area who knows much about this sort of thing.
I could have a dedicated circuit installed with a truly proper ground, but then I read that after the circuit enters the house it may be best to break that ground (hence the isolation transformer), so I am having to learn stuff about things I would prefer to "just work". Oh well. I'd rather be watching video, however.