[Jon A.]

Hmm, bad filter cap somewhere I suspect. You could have a cap that's completely open, causing the vertical retrace to cross-couple into the audio circuit. One time, when I was a lot younger and didn't know nearly as much about what I was doing, I over-volted an under-dash 8-track player, which soon blew the side out of a cap. Good thing the top didn't blow out, I was looking into the player when the cap blew. Running it without the cap caused noise in the audio.