That sounds like either a defective disk or a saved game corruption. I haven't had any reports of performance issues on Xbox or PS2, other than the crash on mission 8 on Xbox. Try swapping your disk out for another copy, then erase the Shellshock save profile off the Xbox hard drive. Then you can either start a new game, or use the level select cheat code below. You can skip to the level you were on.
This also works for those of you stuck on mission 8. Just enter the code, and skip to mission 9.