Marantz AV7701

+1 on what DH said. Likely some other offending player such as a cable or satellite box. You can even try just the coax cable first as that's often the most likely source.

Tsulzbacher, I had same issue with my 7701. In fact, I went through three brand new units and calling tech support as well talking to my retailer. The tech support was not helpful, and said basically they had no idea. I replaced the 7701 with the 8801 and no hum, call support and asked them why, they responded with, the 8801 is a better unit. I never got a clear cut answer, but the 8801 worked fine, and tried the Yamaha CXA5000, and no issues, so stuck with that. My buddy has the 7701 mated with a Marantz amp, no issues. I'm thinking its compatibility issue with the 7701. My amp is a Mac MC205.

I've had the same issue with my 7701, i actually went through 3 brand new units all with same hum. I replaced it with the 8801 with no issues. Called tech support asked them why, and they just said the 8801 is a better unit. My buddy has the 7701 mated with the MM7055 and no issues at all. I believe its a compatibility issue with some of these. I checked all for ground loop and everything came back to the 7701. Called support for all my components and they believe it was the 7701. I went with the Yamaha CXA5000 at the end, cheaper than the 8801 and didnt lose sound quality. For power i have the Mac MC205.

Folks, thx for the help.
I did unplug the HDMI Channel from my comcast HD box and the hum disappeared. Seems, like one of you said, an issue w ground looping.
I would imagine the big challenge now is to solve the ground loop - Other wise my cable box is useless more or less.
Ts

There are ground loop isolators you can buy. At least you've identified the problem. Maybe see if these isolators can fix the problem for you