I didn't notice this problem in the demo, but since buying the boxed copy of the game and installing it the sound system seems to shut down, only sometimes, in between levels. Exiting to windows, restarting and loading the autosave will load up the level just fine. My sound system is currently set to 5.1, with EAX on.
AMD 64 3500+
Nvidia Geforce 7800gtx
Sound Blaster Audigy 2
Windows XP SP2
Drivers and system are current.