Computer Monitor Interference

[sanddrag]

I have three of those black and white compact all-in-one Macintoshes sitting in very close proximity to each other as in this picture Only about an inch separate them. I noticed that when they are this close (within 6") the monitors/screens get a line that scrolls up or down it.
I have a screensaver that just sets the screen to all black, so in this black and white only (no grayscale) crt I belive that means the CRT is not doing anything.

My question is, will the interference between the machines cause any harm to the crt or driving electronics (the power-sweep/analog board)? The black screensaver is on 99% of the time.