I've had this problem in every Vavoom version I've tried. (Note, I've only tried Vavoom with Heretic really.)
The music starts playing, but after a little while it will start loosing instruments and eventually disappear completely. Then as you play on, the drums or some other instrument can come back occasionally and make a few beats before it disappear again.
I've looked in the sound menu, but there's nothing there that allows me to change any sound settings
My system specs.
CPU: Intel Core 2 Duo.
Soundcard: Soundblaster Audigy 2 ZS
PS. Another thing. I'm not sure at what length this is going on, but the game seem to run a tad slower than other ports. The Dragonclaw is definitely firing at a slight slower rate than in any other version of Heretic. It's not my FPS that drags it down, as I got a 125 FPS in my own maps with Vavoom.