My Vibrolux is suddenly making some strange kind of brittle distortion when set clean. I've exchanged the power tubes, but that didn't cure it. The problem is that to date, the brittle sound only happened twice in one specific rehearsal room, and even there, for a couple of minutes it sounds like on the clip, then suddenly the brittle distortion disappears and for the next four hours etc. it's not possible to reproduce it. Now I took it home and played the amp for 3 hours in my garage - everything sounds perfect as always. The clip is here : http://www.soundclick.com/bands/pagemusic.cfm?bandID=495316 Any clue/idea? Do you think the problem could be guitar or guitar-cable related.