i've re-installed my OS, disabled the onboard soundcard...updated the drivers....but all to no use....the problem still persists....
But have you tried reinstalling the drivers? Dunno if that will help or not.
My experience was that if your sound card is doing that, its probably faulty. Although I have fixed one once where all I did was clean the contacts and clean off all the dust (including the port on the mobo and the little holes where the audio jack goes in)
Don't suppose you or your friend has a spare sound card lying around to test do ya?