68kMLA

Solder point shaken loose by bass music?

CRT interference from the magnets would be the cause I believe.

I've noticed it myself when I still had an eMac, but I always wondered if it wasn't caps causing problems. These are known for them going bad, and I figure funny business in the power delivery could cause flickering when the speakers are being driven hard by the amp circuitry.

I sure hope not. I’ve never had any cap issues with my eMac, although it is a 2003 unit, smack in the middle of the trouble zone.