I found the link.
http://www.babcox.com/editorial/bf/bf100326.htm

Pretty interesting article.

On Fri, 09 Jan 2004 22:21:55 -0600, TL <tlehman@visi.com> wrote:

>There was a post within the last few days with a link to a very
>interesting article on rotor warp -- basically explaining that rotor
>warp is generally not the cause of these pulsation problems. In fact,
>he argues that rotor warp is fairly rare.
>