Does it only happen with BO2? Does it happen only on certain maps or gametypes?
If so try re-installing the game, something may have been corrupted down the line.
Have you tried updating your video card drivers?
They release new drivers all the time, and recently added a new driver recently too.
Check to see if anything is running in the background such as:
Virus Scan or something updating.
Hope this helps.
Also make sure you don't have any other games downloading/uploading on Steam while you play. I had a similar issue a couple days ago where it felt like what you describe and it seemed to be caused by a game downloading a patch.