Sounds like some of the parts may be starting to go, or that there is a defect in a part somewhere.
It would probably have to be ALOT of EMI now that I think about it, since the Refresh rate is set pretty low. Tell me, does it still do this when set to 640x480 resolution at the lowest refresh? If so, it's most likely NOT EMI, unless you have an unshielded 50 MW generator sitting right next to the screen
I say if it does it at the low res and low refresh, return it.