Annoying graphics issue

So I'm getting this weird anomaly when I play certain games. It manifests as a weird horizontal bar across the screen then has this flickering effect like it's processing a little slower, or showing the wrong part of an area. It's not really all that bad usually. Usually, when it's there at all, it's just a few pixels or so wide, so unless I notice it (hard to stop noticing it once I do) it's no problem. And besides, there's usually more than enough cool stuff going on that I don't care. But I was just trying to play Amnesia, and it got way out of control. Like a good half inch in width. Kinda hard not to notice it. And it moved up and down the screen too, so sometimes it would be dead in the middle of my field of view. It was making my eyes tingle, so I stopped playing. I really would love to get rid of this thing (I can't play Amnesia right if I'm constantly being bugged by this thing). Thoughts? (And like I said, it's only in some games, so maybe it's a compatibility thing and less of a specific hardware thing. I hope.)