If you have an extra soundcard then you need to put your sound output to stereo (i have to do that on some youtube vids otherwise i have no sound).
Also you can change the decal limit (bulletholes) by creating a hud.ini in your renegade/data folder, all you have to do is to put this in:
decallimit=5000 (256 is standard i think)
i used 10k for a while, the whole map got black after a short time in a 20vs20 war lol
I second what Shai said about the wwconfig, I personally play on lowest detail settings and I still hear all sounds and as far as I remember the bulletholes don't appear on that setting.
I once has an issue with the sound of tanks I used wwconfig, simply changed everything to max then put it back to where it was and that seemed to fix it, not sure why but it did.