70-300 DO autofocus problem - Any ideas?

[westcoaster]

Hi all,
I'm hoping someone can shed some light on a problem a friend is having with his 70-300 DO (the one with the green ring around the lens barrel).
When focusing at a distance (20+ feet) the lens seems to search excessively, making small focusing adjustments, sometimes 5 -6 times before settling on the correct focus (and it is the correct focus, the photos are sharp).

We've tried it on different bodies, same problem, changed up the IS, same problem.
Any ideas what could be causing this, or how to remedy it?

Any thoughts would be greatly appreciated

[neuroanatomist]

If it occurs on different bodies with different subjects, it probably needs to go to Canon.

[westcoaster]

If it occurs on different bodies with different subjects, it probably needs to go to Canon.

Thanks very much.