Hmmmm, not much to go on as far as an explanation so you may get multiple questions before you get an answer.
Have this happens with any other game?
Have you push your game settings to the limit or more?
When was the last time you updated your video and audio drivers
Does this happens often in the game or just in that particular part of the map?
Have you patch the game to the most recent version?
I take it this happens in the Campaign only and not in Multiplayer?
Sorry, perhaps I am not helping you much now and the easiest answer would be to update your drivers and check again... that would be the first thing I would do anyways.