Classe Amp buzzing/humming...any ideas??

I have a Classe CA-151 150X2 amp that has a buzzing/humming sort of sound coming from the unit itself, not the speakers!! It is low noise level (can't be heard across the room) and it comes and goes and usually only last for 1 to 2 seconds. My dealer said it was the power coming thru the wall that had a dip or polarity shift.
Classe said it could be Electromagnetic resonance from the power supply. Anybody have any ideas and/or suggestions?
Sound is wonderful, it does not seem to affect the sound.
Thanks for your input!!
Sounds to me like there's a humming bird trapped inside! Open that baby up and let the little guy out immediately! That should do it :^)
I had a similar issue. Since I knew my amplifier's circuit was on the opposing phase/leg at the service panel, I moved that circuit to the same phase/leg (at the service panel) of my other components. As I was curious to see what sonic benefits would result.

I did not notice any sonic benefits, but that coming and going little amplifier transformer hum went away.

That little transformer hum still re-appears but only when the microwave oven is in use.

Not saying you have the same exact problem, but it's worth a shot.

the 2 prong power cord worked for me as well as switching outlets. Try either.
I had a similar problem with my previous Classe CA-150 and Krell KAV-250a amps. I knew the toroidal transformer was humming, but could not figure out why. After much fussing, I finally found that the 125A service panel for my house was defective. It had some loose connections, and parts of it were literally beginning to burn up because so many circuits had been added. I replaced it with a new 200A unit, and have had no problems since, along with a much lower noise floor as well. If you have the ability to do it yourself, it should cost about $300. If you pay a professional, expect about $1700 to $3000. I decided that was just too much money, so I did it myself, but don't try it unless you are absolutely certain you know what you are can be too dangerous. Good luck.
After the recommendation of Classe, I opened the unit and checked the bolt holding the toroidal trans. and it took about 1 1/2 turns. The problem seems to be reduced. Oh, Glen...there were no birds inside, but thanks for your help! Has anybody ever trie the AH! A/C offset killer?
You may have a DC off-set somewhere. I get the same with my CA-200 when a floor standing halogen light is on "half-power". If I turn it off or to full power, the buzzing goes away.