Wavy Scrolling Can You Help?

Update: After all that, my troubles were down to Firefox. I installed Comodo browser as a test, that was OK, so uninstalled Firefox 13 and installed Firefox 11. No more probs.

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I run two PCs, one new, one not so new, both sharing a common wide screen BenQ monitor.

Prior to two weeks ago, everything was fine, but then I started to see a 'wave' on screen when I scrolled a web page, twitter etc on BOTH machines.

I have changed the line filter, bypassed the KMV, de-powered and re-set the router, tried a different monitor, a different mouse and installed the latest drivers on the new PC, but all to no avail.

The only thing the PCs have in common apart from those things mentioned, is the service itself and the router.

I do not have the same problem with a word document however.

Does my problem lie with the router? People I talk to seem to think it's unlikely.

Can you help please?