It's happened with Mass Effect 1/2, Dragon Age: Origins, and Transformers: War for Cybertron.
NOTE: I wasn't sure how to describe something like this, so I'll put it as best as I can.
Normally, when you turn a TV on to static, you can see a horizontal line usually crawling it's way down the screen. That's essentially what happens in the game. It makes texts and interface flicker, and persists until you either quit the game, or temporarily remedy it with the solution (mentioned below).
Usually the symptom is accompanied with ludicrous amounts of lag. Pausing the game, alt-tabbing, and then going back into the game usually solves temporarily, but the problem likes to persist... a lot. I also attribute it as a primary factor of why I've stopped playing ME2.
At first, I thought it was video settings. Turned the settings down; no go. Problem still showed up. Then, I thought it was my video codes being all screwy again. I'm using the K-Lite Codec Pack, and added them to the exceptions list of the ffdshow codecs (as suggested when I read about it online). Still no go.
For ME1/2 and DA:O, I'd written it off as Bioware game problems. I posted for help on the forums to no avail. So now that the problem has shown up again, I'm looking for aid to remedy this buggering problem.
My specs (fairly drab):
Core 2 Duo e7200
2 GB RAM
Nvidia GeForce 8600 GTS
Windows XP SP3
And my Forceware drivers are running on "Performance", if that helps.