Have a similar problem but it does not appear to be coming from the AC mains. Long and short, tube based phono pre is the problem. If one holds the wires up and about I can actually tune a fine selection of channels through the speakers, and I mean a clear and listenable section of radio stations . Dedicated AC, line conditioners et all did not do the trick. I have been able to repress the noise to a good degree with ferrite clamps. (5-6 bucks a shot at Radio shack) If you go that route clamp everything.... line in out, power speakers, everything.
I have had a solid state phono pre home and it does make a difference. Not wanting to go that route (I really enjoy the tubes with phono) I am somewhat at a cross roads. I can now listen provided I keep the volume down about 10-20db below where I would like it. Basically records are now at best mostly background music. On my proceed pre if I would normally listen at say a setting of 40, best I can currently do is about 20. Somewhere between 20-40 the hum, crackle and then voices of radio hosts kick back in and its all sorta lost.
Best I have found so far is clamp everything in the chain. All cables, speaker wires etc.... everything. This got me a listening volume between 20-30 on a good day.. a little shy if you want to get into something with a bit of bite, but at least useful. At the moment I am waiting on another Solid state unit to see if I can live with it. I also had a suggestion that I try some tube rolling as some tubes are less prone to RFI then others. Thinking of giving that a shot as well. Was wondering if anyone has any experience with this sort of problem and had any luck with rolling tubes?
After talking to a couple dealers in the area, I got a consistent question about where I live, and unfortunately for me, my little town outside of Philly came up over and over again as a problem area. You know.... that ugly feeling when the third of fourth sales guy in a row says "Do you live in.... town such and such", cause we always have problems there. Wonder if we can get real estate agents to start listing this sort of information for the audiophiles out there that have to live with it. :)