Using a Y-cable doesn't fool the electrons .

What happens when you move the 350s physically further from your center?

I've spread them out as far as possible, almost touching my 80's and the hum is still there. It is not real loud, but when everything is quiet I can hear it 12ft away. So whether they are right below the center touching, or 8ft apart, still have the hum, unless I turn one or both of them off.

What happens if you loosen a ground screw on one or both of them?

I'm not aware of a ground screw on the 350's, only the DSP subs.

Oh, good point!

Randy, I'm baffled as to why you continue to expect successful results when plugging things into electrical outlets in that portal-to-hell you call a basement.

Jakeman, calling Jakeman, any ideas.

What happens when you disconnect your cable right where it comes into your house?

What cable are you referring to, the main power supply from the transformer, not sure that would be something our power company would want me messing with, besides not sure that would resolve anything other than shutting down our power. If I was going to do that I would just flip the main breaker.