This is kinda hard to explain but I'll do my best. Suddenly a thin line showed up on the left side and top of the screen, it's very noticeable in bright areas and it doesn't show up in dark areas. I did some research and it looks like it's AA related but I'm one of the few people on earth who keep it disabled as I don't like the overall effect. I think it's a game issue as no other game does it. Auto-adjusting the monitor didn't help at all. Apparently screenshots cut them off so I can't show you what I mean. Any ideas?

Are you using an AMD/ATI graphics card? I have heard of this before with these graphic cards, I do not think there is a fix available for this problem. You can try and contact the Manufacturers, if they get enough complaints they may eventually wake up and realise that people are still playing older games and release some drivers to fix these kinds of issues.

Anti aliasing is what is causing this for sure. Cause It happens to me, and I do have an AMD card. Try adjusting the amount of samples and it may be less noticeable. Other than that, I'm afraid you will just have to live with it.

I hope to someday soon go with Nvidia.