ATI 7200 top of monitor 1 inch distortion on startup
 

Debian Sarge, ATI 7200, Sony Multiscan E200, gnome.
Between the initial text screen on boot and gnome starting, I get a 1 inch + horizonal bar at the top on my monitor. It appears to to be a window running at the wrong frequency.
Will this harm the monitor?
What can I do to prevent it?
How can I find out what the screen is associated with.