Extremly annoying problem

Ive noticed this for ages now, my specs are:
Sapphire HD 3850 AGP 8x version 512MB GDDR3
Intel Celeron D 2.80GHz clocked at 3.3GHz
2 HDDs, not sata
a 2 week old OCZ Technology 500W PSU

my computer, like, perfectly every second it stutters for a split second, but since its happening evey second its very noticable and annoying, it does the on games from worms world part to COD4, and i cant work it out!!!

thanks