If its a very rapid clicking, the clicking will be an injector under the bonnet that injects vapours collected from the petrol tank. i noticed that on my 3.8 and traced it to a small injector on top of the left side of the engine. Its just another environmental thing the americans do rather than vent the fumes to atmosphere. Im actually taking mine off along with the exhaust gas recirculator as it pumps dirty gases into the inlet which ideally needs cold clean air not dirty hot air from exhaust. Hope this helps. Lee
Injector thing at top of pic between oil filler and alternator. Small black box.