fender tube reverb

My Fender Twin Reverb amp crackling noise becomes strong. Tubes?
The amplifier is a 74 'single. Occurred for the first time yesterday, I was playing out of nowhere a loud cracking sound was coming for a few seconds. It also happened when I put the amplifier in stand-by. I also realized that there was a decrease in volume, now would have to rise to 6 to get the volume it would be normal at 4. Usually, it is a sign of the tubes that need to be changed, right? Only I've owned the amp for a year and the last owner said it has been recently rewired. Moreover, a few weeks ago, the amplifier will fall on your face inside a box of roads. That may have something to do with it.
It seems that he broke his pot volume. that would explain both the crunch and declining volume. also fell on his face could explain why so suddenly broke.
1973 Telecaster Deluxe w/added Bigsby into 67′ Marshall plexi 50w & Fender tube Reverb