I second Flavius post.
Just check the other sticky thread on the flickering prob. Some people changed everything in their config but it didn't solve anything.
Btw, it seems a lot of people here are confusing multiple different problems.
Flickering/Quivering : Quick changes in brightness. With VSync on the whole screen will change uniformly, while with VSync off you'll get bands. The frame swapping process is so quick that it explains this difference with VSync off/on.
Seems to be caused by varations of power in the VGA output. DOES NOT SEEM to affect DVI (in digital mode) output.
DVI + VGA adapter will not fix the problem because it's still using the analog output.
Rolling lines : totally different issue. You get waves on your screen. Like on a bad TV reception. This one seems to be caused by external or/and internal electrical noise.
Noise : some components will make audible noise under some specific power requirement from other components.
Personnaly I've seen this problem with a lot of different graphic cards and even some CPU/power supply using Prime 95. It's just a matter of finding the right application.
I'd be glad to go to NVIDIA's offices to help them. Unfortunatly I'm in Belgium.
Well, if one day any guy from NVIDIA goes by Belgium, I can show him the flickering problem and the noise problem on the 5900 Ultra, as well as the "old" rolling lines problem on the GeForce 2 Ultra.
To detect the problem, use a good CRT screen using the VGA analog output. (using a IIyama Vision Master Pro 454 here).
Don't hesitate to increase the brightness/contrast of the screen beyond normal use, it makes spotting the problem easier.
Use the VSync on/off trick mentioned above to know whether you're really seeing the flickering issue or just something else.
The flickering problem happens all the time, in 2D and 3D, but sometimes it's just more obvious.
In my case the most obvious case is when running Unreal 2 in fullscreen mode (1280 x 960 4X FSAA 4X Aniso, Vert Refresh 100 Hz), when in the options menu - you get a strong flickering with the blue transparent background -.
Don't watch the screen for 2 minutes and say you don't have the problem. It took me 24 hours before noticing what was going on, and it took sometimes 2 weeks for some people around here.
I hope this will help.
PS: if NVIDIA is really willing to solve the prob, they can always pay the trip for me and my computer. At least then I'll be really convinced they do whatever is possible to solve the problem.