PC slowing with sound distortion
Dell XPS 8100
Intel i7 860
Nvidia GeForce GTS 240
Windows 7 (64 bit)
Every few minutes, usually 5 - 10 minutes, the PC slows down for a few seconds making everything including the mouse lag, and whatever audio to become stretched and distorted for that duration. It started about a week ago but has become more frequent the past few days. Sometimes the PC locks up for a few seconds altogether and the audio distorts and as you can tell, this is pretty annoying. I've tried thoroughly cleaning out the case for dust and using a disk defragger and a full virus scan, ending all the programs that are taking up the most RAM and a last resort using a registry cleaner, but the problem still persists.
Any help would be greatly appreciated.