Right after I moved my monitor (B&W 17" Studio Display CRT) to another place, I noticed that the screen at 1024x768 75Hz was a little shaky. So, I started to mess around and noticed that the 'shaking' steadily increased as the refresh rate went up. At 1600x1200 60Hz, all is well. Even at the 640x480 67Hz, the shaking is more of a 'wiggling'.
I'm started to suspect this of being interference from something else. Does it sound like interference to you?