Belles amp hum ... rf problem?


Hi all. I have a noticeable hum problem which I have isolated as coming from my power amp, Belles 150a hotrod. The amp hums when I have it plugged into the wall with nothing else attached. The hum is not always present. I'll go a couple days without it and then it will re-appear ... comes and goes. I called David Belles and he told me the issue was likely a quality of electricity problem which was exciting the torroid transformer. (I live in a large apartment building in Manhattan.) He recommends a RF filter. Can anyone recommend a RF filter brand? Would something like a Blue Circle Noise Hound or PS audio ultimate outlet/power conditioner serve this function? If it is a electrical problem I don't think it's coming from within my apartment. I've unplugged everything that I can and the hum persists. Help it's driving me crazy. I may be imagining this but when it does hum the system doesn't sound as good. High frequencies are really grating. Thanks in advance for any suggestions.
tooter
I second Bigtee. I had same problem with a halogen light. On the light's low setting, my amp hummed like crazy. Switch it to the high setting, it basically went away. Toroidal's are very sensitive to this type of stuff.

Regards,
Thanks for the responses guys. Actually I have 3 lights in my apartment that have dimmers but I always make a point of turning them off when I am listening to my system. Is it possible they are putting garbage into the line even when they're off? I think I will try replacing the dimmers with regular on/off switches.

If it turns out not to be something in my apartment causing the problem but say my neighbor. Would something like a power regenerator fix this? I've always been told not to use any sort of conditioning on my amp but I don't think I can live with this hum. If it's quiet, I can hear the hum across the room, 20 feet or so.
One more question ... Are all torroid transformers equally susceptible to this electrical hum? Does it have to do with the size of the torroid or is it more related to how the amp is built/designed? I guess what I'm trying to get at is, in the future if I decide to change amps am I going to have the same problem? Thanks.
just b/c the mounting of the transformer to the chassis is tight doesn't mean that its not the cause.

leave the lid off, next time it hums, go put your fingertips only (carefully! do not touch another thing!) on top the transformer and feel if its a mechanical hum or an electrical one. fingertips are sensitive enough to tell...if the transformer is moving, raise it off the chassis & put some rubber gromules inbetween the mounting plate of the transformer and the chassis.
Thanks for the tip Rhyno. I definitely would not have thought to try that. Hopefully I can get this figured out quickly!

Tooter