Windows Weird sound probs - any help?

Its only just started recently, but im getting a weird 'stuttering echo' sound in certain games and whilst playing DVDs.

Im using XP Pro, and the sound card is an onboard C-Media jobby. Everything has been fine until recently, so im pretty sure its a software or driver prob, but im not sure what.
Like I said, DVDs are all affected by this problem, and the Far Cry and Killswitch demos have also been affected.
Could it be yet another DX9 or Windows Media 9 decoder problem?

Anyone with a previous experience of a problem like this - i'd be grateful for any help.
Thanx.

 

Problem solved - it was a setting in the dxdiag. My sound driver showed up as emulated alongside my old modem driver. Slided both back up to 'full acceleration' and everything is fine now.
Can a mod close this please?