If the sound is missing or corrupted then you may be able to address it by turning off Sound Blaster enhancements.
For example, on Windows Vista / 7 you may be able do this by going to:
Control Panel -> Sound -> Playback -> [active playback device] -> Properties -> Sound Blaster and ticking the Disable Enhancements box, then clicking Ok.
The active playback device will depend on your setup but will probably be called Speakers or Headphones. You may find this option elsewhere, depending on your OS or drivers.
This issue may be addressed in a future driver release or Aliens vs Predator patch.