You don't say what kind of sound card you have, but try going into DXDIAG (from Start->Run) and set the Sound hardware acceleration to 3/4 from Full.
That would probably fix it.
If not, then it could be the sound card is sharing an IRQ with some other device. This would also cause it. Use "System Information" from Start->Programs->Accessories->System Tools to find out if this is true or not.