I bought one of these amps from a guy a few months ago for about half store price. I just had the tubes replaced and the guy I had work on it looked over the whole amp and said theres nothing else wrong with it. (He is revered as the best tube amp tech in these parts) After about another month the amp started making this vibrating sound that kind of sounds like a dead lightbulb when you shake it when I play. So I had him come over again, said tubes are fine probably just the edges of 2 things rattling together on the inside, nothing to worry about. Now, whenever I turn the amp on, regardless of if I have a guitar plugged into it or not, it makes this sound that sounds like radio static. What could it be this time?