S2409W - desktop vibrates when using DVI mode and native res.

I just bought a new S2409W 24 inch flat panel Widescreen monitor.  My video card is nVidia 7800 GT with 252 MB memory, 32 bit interface.  When I connected the monitor to my PC with a DVI cable at 1920x1080 at 32 bit color resolution, the entire screen vibrated up and down.  If I set the display to 16 bit color at 1920x1080, everything is stable.  I thought the DVI cable is the problem. So I connected a VGA cable and set the monitor at 1920x1080, 32bit color res.  There wasn't any vibration.  So it seems only I am having this problem with the DVI mode at 1920x1080 (32bit color).  My graphic card support this resolution at 60Hz.  What could be the problem.

Thanks