Hi, I recently bought two Dell Ultrasharp 2311H monitors for my Mac Pro (1.1). They both show the problem I describe below. Under Mac OS X I get this strange issue with 'shimmering' colors. The effect can be seen mostly in solid color areas, mainly in different shades of gray and blue. The colors on which 'shimmering' appears differ depending on calibration and gamma settings. I also get very noticable and distinct vertical lines in some solid color areas (again, mostly gray). Below is a graphical reproduction of the issue. This also differs depending on calibration and gamma. The problem does not occur at all on Windows 7 run via Bootcamp. Also it does not happen under Mac OS X, when I use DVI to VGA cables (which is not really a solution for me, due to loss of image quality). Judging by these symptoms I guess the monitors themselves are all good. I have the ATI X1900XT. Tried resetting the PRAM, I have the latest EFI for my ATI card. I also tried putting the card in a different PCI slot and plugging only one monitor. Nothing seems to help. This happened under 10.6.4 and is now present under 10.6.5. Unfortunately I don't have an option to test these monitors with another Mac Pro. Might it be my graphic card (or rather the Mac OS X drivers for it) ? Any help and suggestions would be greatly appreciated.