Homebuilt comp freezes in multiple games

[the_ub]

So the issue is whenever i go into full screen games, the computer will just lock up, not respond to anything, and emit this horribly loud crackling-screeching out of the speakers. I have to hard reset it every time it happens. It has gotten worse over time. When i built the computer in feb/march, battlefield bc2 would freeze after an hour or two. I've heard the game had the issue, so i just thought it was the game. Than i got deus ex. I could play the thing for 6-8 hours straight until it would freeze and scream at me. Now, i cant play the game for more than 30 minutes. Ive tried lowering the resolution to bare minimum, and it still froze. BF3 beta didnt run for more than 15 minutes before it would freeze. Now, i know this can be a multitude of things, but i was just hoping someone could point me to what it most likely is, or a few "most likely"s. My vid card drivers are up to date.

system is as follows:
Intel Core i5-2500K Sandy Bridge (with the turbo boost enabled)
ASUS P8P67 (REV 3.0) LGA 1155 Intel P67
G.SKILL Ripjaws X Series 8GB (2 x 4GB) 240-Pin DDR3
XFX HD695XZDDC Radeon HD 6950 1GB
G.SKILL Phoenix Series FM-25S2S-60GBP1 60GB SATA II SSD (with only windows and core programs)
2x SAMSUNG Spinpoint F3 HD103SJ 1TB in RAID0
OCZ Fatal1ty 550W Modular Gaming Power Supply (powering all this and 5 120 mm and a 200mm fan)
COOLER MASTER Hyper 212 Plus RR-B10-212P-G1 "Heatpipe Direct Contact" HSF
standard dvd/lightscribe drive
Windows 7 64 home builders version

and i am using the RAID software on the mobo, and the onboard sound.

 

[the_ub]

Additionally, it almost never freezes outside of full screen games. It has only frozen once; i was browsing the web and my old lady went to plug something into the USB 3.0 plug on the front of the case. The instant the metal of the plug touched the USB port, it locked my computer up. no screeching or noises that time, just would not respond to anything. it wasnt even when the contacts connected in the port, the plug just barely touched the port and it froze. i dont know if it is related or not.