CRT flickering problem

I love my 19" Samsung CRT for a fair number of reasons, but there is a problem that is beginning to bother me, enough for me to post it on these forums. I am not sure whether the video card or the screen is in cause, so I'm posting here.

I can't stand resolutions different of 1024x768 for my desktop, and I have set the refresh rate as high as possible, here 85hz. If you draw a diagonal from the top left to the bottom right corner of the screen, the image is perfect. But as soon as you leave this diagonal and start approaching the evil top right and bottom left corners, there's a notable flicker that's exceptionnaly annoying especially on a bright web page like the one I am using to type this message. Ugh.

Using a lower refresh rate doesn't help, much the opposite actually, and I have tried a couple of ATI Tray Tools options (horizontal/vertical sync) with no success.

What could be the problem? Thanks.