My 06 C Max did the same on a cold start. I had bought it used from a Ford dealer, and returned it under the warranty, but they couldn't seem to get it to re-produce... However, they did diagnose a faulty alternator and replaced that, which I presume meant a new belt. It stil chattered.

Spraying a thin coat of silicone spray on the back (flat side) of the belt, with the engine running, had the desired effect for a few weeks at a time.

Edited by AndyT on 12/03/2011 at 21:30