Help: Audio and Mouse stuttering problem

Hi there, I'm writing here because I really need help with my current PC, built like 2 months ago.

Basically now and then, apparently randomly, I experience mouse and audio stuttering for something like 0.1/0.2 seconds. During this freezes everything is blocked, from the mouse, to the video, with audio being distorted or absent as well. When this started happening it was like 2-3 weeks ago and, 1 week ago, I tried reinstalling Win 7 (64 bit) but nothing has changed since then, as a matter of fact things got even worse: the stuttering now (precisely from today) seems to be more frequent and longer.
I don't know what else to do, please help me  

My system specs are these:

-CPU: Intel i7 950
-Motherboard: Asrock X58 Extreme
-RAM: 12GB GEIL 1600 MHz (used at 800)
-VGA: Gainward GTX 560
-HDD: 2x WD Caviar RE 500GB (in RAID 0)
-PSU: Antec High Current 750W

I've also managed to record the problem, which I think may suggest some kind of problem with the onboard audio itself, though I'm not sure of it. Here's the link: http://dl.dropbox.com/u/14583828/Stutter.mp3

Thanks in advance