i had a similar problem, it was lyk a rattling sound coming from the area where the large vent is near the exhaust. Mine is a 2006 (56) and the dealer told me it was the weight rollers. He told me b4 they were greased into place but peugeot have told them not to grease them anymore so sometimes when ive been out quite far it will make this rattling. He sed it sounds lyk its from the airvent but its from the otherside.
Adam, March 2007