I bought a used Dual Rectifier over a year ago. Sometimes when I have it pretty loud and the footswitch is in use it will literally change channels on its own. If I unplug the footswitch it stops changing channels on its own. I'm pretty certain it can't be the footswitch though because i ordered a new footswitch and cable a while back and I still have the same problem. I have asked a few other people I know with Mesas and none of them have any clue what it could be. If anybody has any ideas I would love to hear them, it's a really big problem when playing live.