It's not just in Mass Effect either, I'm getting them in Fallout as well. Pretty much anything with custom character creation. Significantly, ME is completely un-modded, and that's why it weirds me out.
More aboutstrange artifacts appearing
looks like a driver issue. update to the latest 1s for your gfx. if you are using the latest then try some older 1s also when you ask a question like this please post your specs... it helps us give your better advice.
It probably isn't overclocking or temperature issues, because you get artifacts only in RPGs, but you should make sure.
Few possible things if you're getting artifacts;
1. heat issue 2. driver issue 3. PSU isn't supplying enough power to the gpu 4. If you overclock your gpu