XboX 360 clicking noise while playing black ops?

Ok so theres no unusual sounds when playing any other game (that im aware of), but when i play call of duty, after awhile i start to hear this clicking sound coming from were the disk is. its fine in the begining but after a lil while the noise starts. and when i try to leave the section of the game im in it just goes black and never goes to main menu.. i can still keep playing the game but it makes me wanna turn it off to not cause damage so i save n exit or back out or whatever n it freezes on a black screen. My Xbox 360 is layed horizontal no standing up, and the disk is not especially scratched any more then the little bit thats normal after playin for 6 months.. does anyone know what is causing this, or better yet how to fix it???