It sounds like it could be a engine ping or exhaust shield rattle.If its a engine ping there's only so much the dealer can do.The engine is controlled by a computer that has no adjustments.There has been pinging problems on other chrysler models that was fixed with a computer flash that changed engine timing.There are some basic checks that the tech can do and a tech hotline they can call.I've seen TSB's for other models that states slight engine ping is normal and will not harm engine.