The wiggly monitor syndrome:

"I just got my new computer audio system set up and everything is great except the image on my monitor screen is vibrating. I mean the image is literally oscillating up and down about 1/8 of an inch. It's driving me nuts. What's wrong?"

Standard CRT's operate by using magnetic fields to guide the image producing beams to the proper spot on the screen for making a picture. If another magnetic field of sufficient intensity exists nearby it will cause the image to not paint properly. If you've ever held any sort of magnet near your screen (a practice we strongly recommend against) you've no doubt seen the distortion from its interference. Obviously there are magnetic fields everywhere, but most of them are too weak to mess up your picture. If, however, a nearby magnetic field is oscillating it can cause your picture to vibrate in the manner you describe. This same field would no doubt go undetected if it weren't oscillating, but small movements are very noticeable on computer screens because we are looking at very high levels of detail usually.

Bottom line: you probably have something near your computer screen that is generating an oscillating magnetic field. Look around for anything with fans or some other type of motor, as this is typically the cause. If you have to, pick up your monitor and move it around (while on) a few feet in every direction observing the effect on the screen. If it changes this will give you a clue where the problem is. If it doesn't change it means you have a bigger problem from a source like a big air conditioning unit or large transformer. Some monitors are shielded better than others so if you can't change the proximity between your monitor and the other magnetic source you are going to have to look into a different monitor, or perhaps some radical shielding of the monitor you have. 99% of the time, however, this comes from some small nearby device that isn't shielded as well as it should be.

Occasionally we've seen this symptom caused by fluctuations in the electrical power. These are usually brief occurrences that rarely take on a consistent oscillating quality, but if you can't find magnetic interference this is the second place to look.