AR 150.2 noise

I have a "buzzing" coming from both channels whose pitch is B2 (the B one octave below Middle C). It is present when everything is up and running, as well as when only the amp and speakers are connected. All equipment is running through a PS Audio Quintet which is plugged into a dedicated line. I plugged the amp into a separate ac outlet on a different line with the same results. Swapped power cables, ran a cheater adapter and also used a PS Audio power cable with the ground pin removed - no real noticeable change.

I think I know the answer to this question, but is this buzzing normal for a digital amp? It seems I can hear it constantly, and from a few feet away. Is it in need of a trip to Minnesota? Thanks for any help.
I also have an ARC 150.2, and as long as the pre-amp is on, it is silent, so the buzz is not normal for the amp. I do, however, get a buzz through my speakers when everything but the amp (which stays on 24/7) is turned off, and I forget to set the mute switch on my tubed ARC SP-8 pre-amp to "on," shorting the outputs. I was told that this interaction between the "on" amp and the "off" pre-amp is normal, but has nothing to do with the type of amplifier, merely with the inductance load that the "off" pre-amp presents the "on" amplifier. (Not being versed in electronics, I would have to find the thread to provide the explanation that more knowledgeable forumites gave me.) But, to be clear, when everything but the amp is off, and the mute on the pre-amp is on, everything is again silent, and when the system is running, there is no background noise. (In fact it has become a bit of a joke in the house that the system is so quiet that on the silent tracks on LPs, I tend to get up early, thinking the record is over.)
Thanks for your help. I am going to try one more experiment - I'll take the amp to my neighbor's house and hook up my speakers to see if the buzz is still there. If so, off to MN.

I still don't totally trust the a/c in my home. It's an old place with mostly updated wiring. The circuit for my audio equipment, however, is a dedicated circuit. I just hope there is not enough noise in the wiring to cause interfernce in this dedicated circuit.
I also have the 150.2 and have not experienced the problem you describe. So, to answer your question it is not normal for digital amp, at least not the 150.2.
My question is has the noise been there every since you had the 150.2? If not, then it probably is the amp. Also, if the noise is there only when the amp is powered up, then again it is probably the amp.
I like Palewin leave my 150.2 on 24/7 and when everything else is off, dead silence.
Just as an aside, it might be useful to also check your preamp as well to be 100% sure.

I can't honestly say the amp was doing this when I bought it, but I do know now that I am really noticing it. Since then I have upgraded other components and changed speaker cable, so maybe this combination of things has allowed the buzzing to be more easily heard. There seem to be times when I can hear it from my couch, which is about 6 feet away. However, I don't know if it is really that loud, or I just know it's there and therefore it seems that loud.

Thank you both for your input.