Does the C22 have a three prong power cord? What I mean is that , this could be a ground problem. I kept thinking it was a piece of my tube gear as well..(it wasn't) Are you using multiple components plugged into a few different wall outlets?? If so, combine them down to one, using a cheap power strip that is grounded (three prong). (I had a very similar noisy sound with channel spikes) Good luck.
Matt
Matt