Very Computer

I'm trying to get X to work with an ATI Mach64VT 2mb (newly supported in
RedHat 6.0) with an old Sony Multiscan 15sf (no longer appears in the monitor
list of Xconfigurator).  I know what monitor settings worked for me before:

Horiz refesh: 31.5-64
Vertical refresh 50-120

However, this setup doesn't seem to work well.  Half of the screen looks
"fuzzy", like static.  The other half of the screen looks perfectly fine. Does
anyone use this card/monitor combination? Has anyone heard of a problem like
this?  Answers or insights are appreciated!

Thanks,
John