computer freezes

I've build a new pc like 3 weeks ago, and I'm having some weird freezes.

Here is a configuration:


During games (ranging from Mafia 2, Bordelands, D3 and even LIMBO) I get screen freezes for a couple of seconds mostly and then the system recovers and continues onwards like nothing happened, no errors nothing shuts down, nothing. On 1 occasion it didn't recover and I had to manually reboot my pc. Also When the image freezes there is noice coming from my speakers, as can be heard in the video that's included.

I've checked my memory using Memtest, nothing to be found.
I've checked my GPU for odd temps but it doesn't go higher then 75° on load so nothing out of the ordinary, even right after crashes no exceptional temps found anywhere.
I've done a short run of Furmark and that didn't take my GPU higher then 79°-ish so nothing there, although it didn't run for hours, no artifacts nothing.

I then suspected the PSU so seeing it's modular I swapped the cables and connected everything to other sockets. I didn't get problems for a while but seeing I thought it was a faulty PSU port or cable I still took it back to the store to avoid problems down the road, they checked the voltages, connections and everything, nothing wrong with it apparently.
They told me it might be corrupted sectors on my HDD and said to check that with HD-Tune, but that didn't turn up anything.

So reinstalled my PSU just like before, changed nothing and the problems didn't occur for a week or so but now out of the blue they're back.
It happened again today and here is a recording of a crash in progress:

http://www.youtube.com/watch?v=W4Owqp1oJhw&feature=youtu.be
(sorry for bad quality, the sound you're hearing is the noice from my speakers)

Hope you guys can help.

Yes, but then again is playing LIMBO putting a machine under stress?
And It doesn't occur on regular timing say after hours of playing, it can happen after 15 mins or after 6 hours.
No freezes in Windows or while browsing or stuff like that ( my main reason why I suspected the GPU)

Latest BIOS update and AMD catalyst drivers installed, but the store where I bought the setup told me to roll-back my AMD drivers, saying the newest drivers aren't 100% compatible with older cards and it's better to have drivers from its own generation, any thoughts on that?

I'm going to try the on-board graphics, but any idea how I could 'stress' those can they handle any games?

I could try an other PSU, from my brother or a friend, I'll try that if the on-board GPU doesn't change anything.

thx, for the quick reply.

It just happend in Windows, and I'm on my onboard GPU, now what?

it's not my memory (afaik, memtest didn't show any problems), not PSU, not GPU.
could it be the CPU?