Sandy;
I recently experienced what seems to be the same thing on my 180 2.8
lens. I took it to Nikon and what they did was this:
They put a very small bit of oil on the rotating screw on the mount of
the lens. If you hold your lens so your looking at the back and rotate
the focusing ring you will see this little screw turn as you focus.
They said it had become dry, and all it needed was a little oil. They
did this at no charge while I waited. The screching noise went away and
has since not returned.
Hope this helps,
Sam
