Annoying Stuttering! Help!

Hey. I currently have a big problem.
All my games run at max with more than high enough fps..BUT in some games lately I'm getting stutters all the time. Like once every fifth second it stops for about 0.5 seconds and on and on. Games are unplayable like this, and I wonder what the problem might be.
Check my system specs for info on it!
Even in WORMS!! lol. I mean something is clearly wrong here, I've tried going back to the previous nvidia drivers, but didn't work. I really don't know what's the cause of this problem, so it's hard to do anything. Maybe realtek integrated sound is the problem? I have no clue here, please help me out!

I'm using Nvidia drivers and I have already updated to 0901. Still the same.

The Howling Wolves: Well i recently finished assassins creed 2 and that game didn't have this problem, it was flunky smooth all the way, this is just for some games, so I think it's seated just fine. I tried disabling SLI, still the same, tried disabling soundrivers, still the same, ran it in vista compability mode, still the same and I tried changing resolution and graphic settings, still the same old story. The only thing I can think of would be some kind of setting in the nvidia control panel that messes around with the games..

Lemur said:

Do you have your card OC'd?
Check event viewer for hardware events.
Might tweak Nvidia Forceware
TweakGuides.com - Nvidia Forceware Tweak Guide

Why when I look for your card on NVidia's site I find this:
NVIDIA DRIVERS 258.96 WHQL
Compatible with GTX 480

I don't have them OC'd, they are on default.

Yes, that's the driver I use right now.

Scanned my pc with malwarebyte, found 1 error, some kind of forced display thingy in registry, don't think it will make much difference.
Guess I could try to defrag my OS disc too, just to check if it helps..