Oblivion distorted texture pop-in

[Prenihility]

I really dont know how to explain this, im not even sure how... Basically, im finding some sort of strange shapes (looks like a texture problem) popping up in the game, usually when new cells are loaded, and when loading is done in exterior cells.

 

Basically they are stretched out black rectangles. Whats causing this? I didnt install anything new, nothing has changed.