I have noticed it on my Roadster. When I brought mine into a tech to have it checked out, embarrassingly the hum went away. The tech told me often times power supplies can do that to an amp. Of course, I went home (drove an hour to have the thing looked at!) after having the tech tell me everything is fine with my amp, and when I plugged in, voila, the noise is back! It is the slightest little hum, but I concur with the tech that it must be the power supply in my apartment complex. It is an old New England apartment complex, with updated and renovated amenities, but these very, very old power supplies in the walls. Anyways, I am going to invest in a power conditioner soon. Maybe, just maybe, this is the case with you amp?
