Probably a short in the flyback.
Take the center spindle out of a roll of paper towels, then with your head carefully away from bad things like the tube neck and the neckboard, point the spindle towards various spots on the chassis listening to see where it is the loudest. I'm betting it is in the flyback.
Does the picture ever appear, with just a snap shrinking the size and back, or is it a dead screen but with snapping?
If it appears, you may be able to temporarily fix things by jamming a toothpick or two into the top of the flyback (with it off obviously) to keep the core centered. But that is normally more of a small crackle than a loud snap.
Good luck