Last night my Peavey Classic 30 made a loud thump/fart sound when I turned it off. It was on low volume in the normal mode. It has never done this before. It did it with the guitar pugged and unplugged as well as with my 2x12 cab plugged and unplugged It was much louder with the cab plugged in. It seamed to happen after the lights went out in the tubes, not when I first hit the switch.
Thanks for your help.