Sound problems with a new Geforce Fx5600!

just got a New Geforce Fx5600 and installed everything. All is sweet till I boot media player and things go haywire. It seems that moving images seem to distort the sound. If I minimize media player (with the dancin lights and stuff hidden) then it sounds fine (so long as I don't move the mouse), as soon as things start movin on screen it goes really crackly.

I'm using a 1.2GHz, 248MB RAM with onboard sound, and the 5600

any ideas why things are goin face up?

Thanks
Awful