Fiddling with settings didn't do anything. However, just today Nvidia released new drivers that fixed the problem. Talk about good timing! (Of course if they hadn't screwed up the drivers in the first place...)

But I have some music problems, similar to what's mentioned in your FAQ. Most of the time the music plays fine, but sometimes after beating a boss, or when the music changes to boss music, or finishing a level, the music does not restart. But sometimes it does, even after playing a level without background. Very intermittent.

Sometimes I can start the game with no music!

Sound effects are never effected.