Since replacing the high gain side cliff jack back in may, I've put numerous hours on the amp with no problems whatsoever. 

I have a 2204 that I bought from Nik last year, and I had only played it a few times at the house because of the volume. The sound is absolutely superb.  A few days ago, I used it at an outdoor gig. Playing through the high gain side, it played fine for about 20 minutes, then in the middle of a song, it started humming loudly like when you put a finger on the end of a guitar cord tip. I quickly checked my connections which were all fine. I pulled the guitar cord and plugged it into the low gain input and it played fine for the rest of the show. The next day, I plugged a guitar into the high gain side, and immediately got the same loud hum. I removed the cable and inserted it again and the hum went away. I even let the amp sit powered up for a while in case it was some sort of heat related prob, but, was unable to duplicate the prob again. I checked the ground wires from the jack and they appeared to be fine. I'm thinking maybe the high gain channel cliff jack has an intermittent prob or is dirty/corroded perhaps. I cleaned the jack inside with contact spray as a precaution, but, other than replacing the jack for arguments sake, does anyone else have any ideas what may be amiss?

Replaced the high gain channel cliff jack and played the eff out of the amp for about 2 hours. No problems