Diagonal waves running across the computer moniter

I have a new recently purchased PC(running on XP) and a new screen, which has a problem of diagonal waves running across it. They show mostly while viewing different shades of grey, but the phenomena is not consistent – sometimes it goes away and then returns. It doesn’t seem to be a monitor hardware problem – it’s been taken to the lab and plugged to other computers in other rooms and it worked fine – no waves. Only when it’s placed in my office the problem occurs. I also tried plugging another monitor to my computer and got the waves…
The reason must some electro-magnetic interference at my work station. Has anyone ever ran across a same problem? All suggestions or comments are more then welcome, i’m a bit lost here…