Turns out the amp has always popped. Man, that pop is annoying and loud. Seems it should be pretty easy to get rid of. I wonder why Fender would not take care of that?

Thanks. I will have another look at it. I did notice the two large 3300uf electrolytics that I had to resolder still contained voltage when the unit was off for a while. Maybe I'll start by replacing them.

My friend gave me his amp to try and fix it. It was humming like a mother and there was a crackling when the guitar is played. I fixed that. It was 2 large electrolytic caps. Replaced them and it is dead silent and no crackling at all. Now there is a loud pop when I turn it off. Turning the volume down before turning it off doesn't help. Any suggestions?