Precision T5500 & Intel Matrix Storage

Hello everybody

Recently I bought a new Dell Precision T5500 with a Quad Core Intel Xeon E5640 @ 2.66 GHz. It came with 6 GB RAM and an ATI FirePro V4800 graphics card.
I upgraded the machine to 18GB RAM and an ATI Radeon HD 6850 in oder to make sure I got some serious graphics power and enough memory to make swapping a thing of the past.

Running Windows 7 Ultimate 64, everything was super-smooth and fast until I tinkered with the built-in Intel Matrix Storage Manager. I got an additional 1TB HD and configured RAID in the Storage Manager. Unfortunately, I set up RAID 0 stripping so effectively created a volume with 2TB combining the two WDC disks. That wasn't exactly what I wanted as I realized after restart that I actually wanted a RAID 1 config but pressed some wrong buttons. Well, I ended up deleting the RAID Volume and reinstalling Windows 7 and everything again on one HD.

It was then when I realized crackling sound-playback from any application. The crackling, skipping seemed to occur pretty randomly but I could nail it down to occasions when the USB WLAN Adapter was pretty busy in either downloading or uploading or when copying big files from HD to HD or installing applications.

The problem became very annoying as I couldn't listen to music anymore on both the internal sound-card (using headphones) and USB Harman Kardon Sound Sticks - these skips, crackles and distortions vere just to frequent and intense. So I began googling the problem what pointed me pretty quickly to this being a DPC (Deferred Procedure Call) Latency issue where a driver uses to much time on a function. To check latency times on my machine I downloaded the DPC Latency Checker and the app clearly displayed the high latency spikes from time to time. When playing music or copying files/installing apps the bars wouldn't recover from the red field until the copying finished. Unfortunately, that tool didn't nail down the spikes to a specific driver so I found a program called "LatencyMon" from http://www.resplendence.com/latencymon which could tell which driver used to much time. Look at the list:

http://tjh.ch/dell/latency.jpg

So you see the Intel Matrix Storage Driver (iaStor.sys) using up to 797 ms to execute.... 0.8 seconds (!!!) where usually a driver shouldn't be using more that 100 microseconds (!!) do respond so I heard.So I tried to use different versions of the driver from Intel with no success.

Currently the Intel Matrix Storage is set to RAID in the BIOS. But I tried using AHCI and ATAPI with fresh Windows 7 and even Windows XP 32 installs with no success.

So now my question - did anyone else experience the same issue with similar hardware and does someone even have a solution or some ideas what I could try to do?

Thanks and best reagds
Thomas