My FPS decreases when i move my mouse!
Plz i need help, When i move my mouse, my FPS decreases in INTRO SCREEN and IN THE GAME. I already tried everything and nothing.

My System:

AMD Radeon HD 6900 Series 1024 MB
Processor: Intel® Core™ i5-2500 CPU @ 3.30 GHz 3.30 GHz
RAM: 4.00 GB
System: 64-bit Windows Seven