My Toshiba 34HF85 has started exhibiting a rather annoying problem. Sporadically, through both the component and HDMI inputs, these a bunch of thin black and white horizontal lines will flicker on the top third of the screen and then disappear. They make the whole picture jump a bit, and they distort the image where they appear. It seems almost like electrical interference to me, but the lines are much more pronounced than the sort of wide faint lines I've seen on other TVs when that's a problem.

The only description I found online of something similar to this was related to something the person called "vertical shielding", but I don't think there's a setting in the service menu for that.

I don't think it's related to the center channel of my surround sound system sitting on top of the TV (since I've tried lifting it off of it, and there's been no change), but I thought I'd mention that.

This used to happen very rarely and only when I using the TV for a long time, but the past few days it's happening every couple of minutes and is very distracting.

Anyone have a clue on what could be causing this?

This issue is most likely caused by a failing flyback transformer. It's either got bad soldering on the board (which is easily fixable) or the coil could have some insulation issues causing periodic shorts, in which case you'll need a new flyback. They aren't too expensive but special care is required to change it since it outputs 27 000 volts, and that kind of voltage could easily arc and blow up the whole set if the soldering isn't done properly.