strange flat chassis Zenith problems

[Adam]

So for the past week or so, whenever I turned on this TV (25EC58 in the Avanti cabinet), after a few minutes I would start seeing white horizontal lines of varying thickness intermittently flashing across the screen. So this afternoon, I turn the TV on its side, and start poking around trying to locate the problem. After a few hours (I still hadn't figured out what was causing it) but it went away on its own. I figure I'll leave it apart for a while and see if it comes back. I'm hoping it doesn't, but does anybody have any idea what it was?