My car is emitting a chattering that is only audible when the car is moving (regardless if it's in gear or in neutral). It comes and goes. The car drives normally. At first I thought it might be the catallytic converter's heat sheild...but the problems seems to be a function of car speed and not motor rpm (I've coasted in neutral and I still hear the chatter).

Any ideas? CV joint (I don't notice any difference while turning...I notice it mostly while going straight)? Do you think this would be covered under the 5 year powertrain warrenty?