My daughter's PC has intermittent sound when playing back music. My wife has the identical computer (gateway laptop) which does not have the problem.
I have already antivirussed, antispywared and defragged. I notice that when monitoring using PERFMON that the bad computer has periodic CPU usage spikes whereas the CPU usage is low and constant on the good computer. I've tried to look at the processes page to see an offender but it seems like system idel processes are the only thing that spikes up on the bad computer.
More aboutintermittent sound
Download the newest drivers for the sound card/chip. This should fix your problem.
If nothing else works, you may want to back up the music and any other important files and do a restore/reinstall of the operating system. Then make sure Windows and drivers are all completely updated to the latest versions.