#2
My amp does a similar thing every ones in a while (although not nearly as bad as yours). Try leaving it unplugged for a while (several hours). It works for me.
#3
https://www.youtube.com/watch?v=07HXs2VzFyM





Sounds like a diode crapped itself. Not an easy fix.

You could try swapping the tube(s) out. That's what I'd do and it should be pretty easy but I have no familiarity with your amp. I have a video on how to do that if you are interested. Good luck.
#4
Probably one of your tubes going bad.

Replace both the 12AX7 and the 12BH7 tubes.
My Gear:
Fender Classic 50s Strat
Gibson Les Paul Studio
1977 Marshall JMP 2104
1995 Marshall 1959SLP
Silvertone 1481
Yamaha RA-200