It's been mentioned in this thread, but I felt it was worth starting another thread because it seems there was more than one audio bug being talked about in there.
Basically, the problem is, all music stops playing.
If the player notices the music has gone and is not in a cut-scene, it can be restored by saving, quitting the game, then reloading. But it usually happens while switching tracks, so players (or me at least) might not even notice and think a room or a cutscene is supposed to be silent.
If it helps, after having it happen to me three times this season I think I know how it is triggered: Basically you have to play the game non-stop for about three or four hours.
Yes, OK, I know playing that long is not healthy. But it's your own fault for making your games so addicting. =P