I've got a pair of Dell 2009W displays at work, plugged into an NVIDIA Quadro NVS 295, using DisplayPort to DVI converters.

I'm seeing a little bit of something that looks like "dot crawl" on the monitors. It's more pronounced in the top-left corner of the right-hand (secondary) monitor.

Any ideas?

I have the same setup, except different monitors. I have also had a problem, though it is significantly different from yours; one of my monitors blinks out now and then. But I found that my problem was related to the dongles. Try swapping them around and see what the problem follows.