Thanks all. Here is the sub cable I am using: a gray Monster Z High Resolution Video Interconnect Cable. About a meter long. "Video" cable can't be that much different than audio - can it? Maybe I'll go out and get a nice shielded audio cable.

Back to the original problem, it seems that the grounding on the cable splitter in the basement is fine, I might just need more shielding on the sub cable.

Interesting, yesterday, looking at audiophile sites. I came across a comparison of cables and Monster tested at the bottom, in one review, worse than the "stock" cables that you get packaged up with components. Maybe Monster is a bit like PIAA - great marketing but not the real deal (everyone see the bulb test in the latest Roundel?). And I came across an article that recommended that cables be up off the floor.

I'll look around today for a good sub cable and, ncx, thanks for suggestions on the line conditioner. Suggestions on a non-Monster sub cable?

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Trex