You ain't the first and you won't be the last Baldie, it's a sound error, it's starting to creep back into my game after maps change sometimes too, but it is ok after i reload map, there are many possible fixes, many have been posted on the website over the last year or so, the one that usually works for me is to update your sound card drivers, but if this has just started to happen after you have updated your drivers then you may have to roll them back, if the problem gets really bad for me i uninstall cod4 then update drivers, then re-install game back to my new drivers and that always seems to work, but many don't like doing that because they might lose their stats etc, it don't bother me i would rather have the game running smoothly then worrying about stats. Also been told this problem only occurs if you have a Nvidea sound card, i have no first hand proof of that but it has made me think of getting a new sound card