From the details you give here I assume that your fairly up on kernel options etc - sound, USB, ethernet etc. so I'm assuming these are OK.
You don't say which flavour of sound drivers you're using but if you're using nvaudio you
could try the ALSA drivers (free on Linuxformat coverdisks) or Opensound drivers (fairly cheap) from http://www.opensound.com
The other option is to try specifying some options in your /etc/modules.conf file for the sound driver you're using - you can assign a different irq & IO settings etc.
Does this make any sense ?
Good Luck !