ATI Radeon 8500 problem (or the ViewSonice A90f+ monitor problem)??

Hi, all:

Thanks for reading this post. I have a custom made PC which is using
Epox 8RGA+ motherboard with onboard video (nVidia GF4 MX). I run dual
monitors setting (two ViewSonic A90f+ CRT monitors). When I'm running
these two 19" monitors with the onboard video card, everything seems
to be working fine. Recently I got a used ATI Radeon 8500 video card
and put it into my current setting, now, for some reason, the second
monitor will flash with some light thin "strips" when I scroll down a
long Web (or MS Word) documents. This problem become more apparent
when the long Web page has a pure white background. Here are my
questions:

1. Is this a problem with the ATI Radeon 8500 video card? As I didn't
experience this kind of problem when I was using the onboard nVIDIA
GF4 MX videos (also running as dual monitors setting).
2. Could it be a problem with the monitor(s) themselves??
3. Any trouble shooting tips or solutions?

Thanks!