Rippling effect when moving windows or scrolling

[TerryJ]

I've got Xfce 4 (version 4.3.99.2 (Xfce 4.4 RC2)) on KateOS 3.2, where 
it's the default desktop.  Now I have to use fuzzy language.

When I scroll on a page, the page seems to have a wave moving below it.  
It's like watching a series of related camera frames in sequence, or 
slides.  It's very distracting.  A similar thing occurs when I move a 
window.

I cannot find any relevant settings and don't know whether the two 
things are related.  Does anyone have any ideas?

-- 

Regards, TerryJ

Using Xfce on PCLinuxOS 0.93 and KateOS 3.2. www.revivalcentres.org