Sound locks up and repeats

Greetings everyone,

I have no idea where else to turn before sending my computer back to the vendor. What happens is that every time I put a game on, either it's DirectX (i.e. Star Trek Online) or OpenGL (i.e. WoW), at times the sound locks in a loop for a few moments and then continues. Several of those times the display locks as well, while other times it doesn't. Crashes occur randomly. I have tried everything.

The system is three days old and it has the latest drivers from every manufacturer. Here's the setup.

CPU: Inter Core i7, 2.66GHz
RAM: 12GB Kingston ValueRAM
Motherboard: ASUS P6X85D Premium
GFX: Shapphire ATI 5870 1GB VRAM
Audio: Onboard Realtek HD audio (tried with Audigy 4 PCI card, same results)
System HD: OCZ-Agility SSD
2nd HD: Seagate 1.5TB
OS: Windows 7 Home Premium
Power Supply: 1000Watt Coolermaster Silent Pro M1000
Case: Coolermaster Cosmos RC-1000

The OS has only drivers and Avast antivirus installed. Max CPU temperatures do not exceed 60degrees celcius (140F) and the GPU never goes beyond 54C (129.2F). Mainboard temperature stays between 30-32C (86-89.6F).

The display driver is the Catalyst 10.1 (8.69). The audio driver is directly from Asus' website. Latest chipset and SATA drivers are accordingly installed as well. Latest DirectX (Feb 2010 Redist) is also present. I've tried with virtual memory on and off. Same results.

Can anyone help, please?

Thank you in advance!