I started getting this when I went from onboard sound to Audigy 2.
Try downloading the latest NOLF 2 patch (version 1.1 was supposed to fix some sort of sound bug). I haven't gotten around to patching it (playing other games right now), but I'd like to know if you resolve the problem.
Worst case, if you turn the sound settings to software (i.e. no hardware acceleration), you'll probably be ok.