You say no input, but does that mean your C50 is on at zero gain? Should be on at zero gain and preferably a non-active source. If so, do the isolation drill by powering everything off, removing the ICs from the amps and turning just them on. If you still have the pop/hum issue, try different outlets in the house. Go so far as to move the amps to different rooms if you continue to have issues; there could be a device elsewhere in your house that's creating noise. If all of that doesn't seem to make any difference, you may have some kind of problem with the main house ground or sadly, with the amps themselves. No way to know that without getting the amps out of the house onto a completely different main circuit.
Good luck!
Good luck!