I had the same problem with my Super Vs re: Noise. Fixed it with a P.I. Audio Buss, TWL power cables, rewiring my mains outlet, removing the 300B amps I had in my system and replacing them with a Neurochrome (Mod-86) amp and being very careful about wire routing. My A370 amps still hum, but its transformer hum (not coming through the speakers). I can hear it *just barely* from my PLP, but as soon as the music starts, it gets masked.
I've worked hard to make my room as quiet as possible this past year, which is a double-edged sword. I had an older MacPro tower in there, which was the primary noise source. That got replaced with a silent mac mini. All of my spinning drives were replaced with SSDs as well. I've done a lot with acoustic treatment both outside my room (I'm in a finished attack and was able to wrap my space in Prodex and further insulate the walls and ceiling. So all this is well and good, but you start exposing other noise sources as you get to that last 5% or so.
After all that work was done, the next loudest noise source was actually my NEC monitor connected to my Mac Mini. That was replaced with a much quieter ViewSonic monitor early this year. Now what's left is the slight hiss that comes through the P-Audio co-axial drivers and the transformer hum from A370 amps. I haven't done a background noise measurement in a few months, but I should repeat that. I've experimented with isolation transformers between the A370s and the output of my PS Audio DAC. They seem to help with the overtones of mains noise that are coming through the 12" subs -- 60/120/180/240 Hz.
But you can end up driving yourself crazy trying to chase all this stuff done, and as I said, as soon as the music starts playing, it is all masked. But that is much of the fun of this hobby, isn't it?