Crash to 'no signal' and brief sound loop, otherwise solid system

Hi,

I am having what seems to be a common problem for some ppl: an apparently solid system that crashes reliably in some games. The crash is to a black screen (no signal) with a sound loop that lasts perhaps 20 seconds. I *believe* this is a BSOD, but with the graphics driver dead.

What I have tried so far is:

- Furmark stress test (runs at 75-77deg for over an hour without a crash)
- memtest was ok a few days ago
- heavy CPU workloads (all CPUs at or near 100%) does not cause an issue
- 3DMark tests. Run fine.

Typically when the game crashes the CPU is around 40 deg, the MB at 30 and the GPU at 68.

Again, typically, before the crash the graphics will start to stutter intermittantly (freeze for 1-5 seconds every minute or so with decreasing intervals).

As I said before, the system is otherwise rock solid.

Key differences in games to my normal heavy workload:

- direct x (my normal workloads are just IO & CPU)
- heavy graphics use
- lots of use of built-in sound card (SoundMax)
- use of USB headset (for voice)

The system is:

HAF Case
i7 920 CPU
Altec 850W PSU
4870 GPU/ 1GB
6GB G.Skill memory
P6T Deluxe MB

One other data point: when I use ATI Overdrive to set the GPU and memory speeds to minimum, the game crashes a lot less. But still crashes.

Any help or suggestions would be greatly appreciated!