There are a number of reasons for screen flicker. Here are a couple troubleshooting suggestions:
It may be that system activity is memory-starving the display controller; see topic 88 for details about correcting that issue.
You might also have a cable problem, especially on the HSYNC or VSYNC lines; try wiggling the cable to see if you can reproduce the problem, or re-seat the cable to make sure it's making good electrical contact.
The flicker issue happens with neither ethernet or CF cards installed. No applications are running. We have tested the same issue with five different units. The cables seem to fit well and wiggling the cable doesn't exacerbate the problem.
1.) No apps are running - does this rule out the starved memory question?
2.) It happens in multiple units (in multiple environments).