Computer Stutters!!!

[ZildjianAVC]

Hello wonderful community.

Periodically my computer will start jittering (freezing for a millisecond) at a regular rate of every .4 seconds. It effects audio, video and my mouse (although audio is the most audible because the glitches only last a very short time). But this happens when only a few basic apps are running, AND it doesn't necessarily happen when I have Prime95 running. That said, it happens mainly when the CPU is being used, and does not happen consistently (it may go away for 5mins, then be bad for 5mins, with no external changes).

I'm running all the latest updates, and other than this my system has been running fine.

Specs: i7 920, 12GB DDR3 Corsair XMS3, GA-X58A-UD3R, MBox 2 Pro, 5.5TB WD Black, GeForce GTS 250, Windows 7 64bit, Antec EarthWatts 750W

Ideas? I don't know where to start!

Thanks!!
Z

Edit:

 

[Hefemeister]

Any overclocking? If so set it back to default to see if that eliminates the issue.

run memtest to check memory.

 

[ZildjianAVC]

no overclocking - in fact my 1600 RAM appears as 1066.

Ran Prime95 for over 10mins while running StarCraft 2, chrome and mumble, no problem.