Problem with Onboard Sound

Hi, I've recently been having problems with my Media Center 2005 system I've built.

It's a Ideq 210v shuttle system with a onboard AC97 sound card (CM19739A - c-media).

It's been working fine for weeks, now its gone alittle strange. All I can hear is popping and scratching. Playing with the 3d sound proggie that gets installed with it.. I can get the sound fine using just the righthand speaker - but the left is very distorted.

If I switch it to 4 speaker mode.. the front speakers will work - but again, not the left. It's certainly not a speaker issue as its playing through the tv.

I think its something to do either with the motherboard itself.. or some corrupted files !?.

I've reinstalled/upgraded the sound card and motherboard drivers, everything like that - but the distortion is still there.

I've totally ripped every setting out of the reg !.

I've installed another soundcard into the pci card as a test - this seems to work fine !. I cant leave it there though as its for the TV capture card. (darn shuttles with their 1 pci slot !!!)

Any help please.. or perhaps some suggestions on how to track this problem down.

Thanks !.