Low level buzzing coming from tweeters.

 I have a pair of atmosphere m60s and had that problem and it turned out to be an input tube.  I also have a LuTron dimmer in my room and whenever the lights are on I get a little buzz as well.

Gotta be the amps?

Yes.

@atmasphere Thanks for the confirmation.

@analogluvr  At your suggestion, I changed the input tubes. No luck. I also have a Lutron 4-zone dimmer, but no change with the lights on or off.

Very frustrating, as you can imagine.

At a friend’s suggestion, I ran a long extension cord from each amp separately to an outlet at the other end of the house. There was now a barely audible hum that could not be heard about 2 1/2 feet from the tweeters. My listening position is 12 feet from the speakers and the buzz, which I now better describe as a loud hum, was loud enough to be annoying . . . and aggravating.

This makes more sense to me as I presumed the odds of both amps having the same exact problem to be unlikely.

Next stop . . . an electrician.