Random CPU spikes in D3, Fallout New Vegas, Dawn of War II . . .

Hi all! I was here a few weeks ago for help with a BSOD problem. You guys were immensely helpful, so here I am again.

I'm running a custom built machine.

Intel Core 2 Quad, Q6700 @ 2.66. GHZ
4.00 GB ram
MSI-7380 Mobo
NVIDIA GeForce GTX 560 Ti
Crappy onboard RealTek high def audio
2.5 TB of HDD space
Windows 7 Home Premium 64 bit
MSE antivirus

Here's the problem. When I'm playing certain games (Fallout NV, Dawn of War II, D3) the game starts out fine. About 5-10 minutes into the game I will get freezes/sound stutters that last about 2-3 seconds. They get more frequent as time goes on. If I restart the game, they stop and come back.

I'm at my wits end, here. I don't think it's a hardware related problem since I can run some games -- Skyrim comes to mind -- with no problem. I can leave the damn thing running all day. Skyrim is obviously a much more resource intensive program than Fallout NV, so I don't think it's a heating problem.

I have a hunch that it's audio related, and that my RealTek is causing a problem. I installed the latest mobo-specific drivers for it today, but no dice. All of my drivers (and I mean ALL OF THEM) are updated.

How do I start troubleshooting this? If I leave resource manager open in the background, and boot up a game, can I wait until I get a spike, close it, and go back to the manager to find out what process is causing this huge spike?

I ran CCleaner, and Registry cleaner. I also uninstalled a whole bunch of junk I wasn't using.

Any help would be appreciated.

UPDATE: I disabled my audio completely and started D3. It ran for about 5 minutes and then the shenanigans started again. So it isn't audio . . .

i suspect a memory issue, have you tried memtest86? here's the link, you'll need a spare CD/pen drive to run the test
Memtest86+ - Advanced Memory Diagnostic Tool