Well it certainly sounds most likely to be the differential. However if it is a resonance problem would there be a way to decrease the vibration from the heat shield myself? Possibly dampening the noise? Thanks.

However I just put in a service request at my local Chrysler dealership for Thursday afternoon (keep your fingers crossed its my first time using them as I just purchased the car last week). Armed with print outs of repair orders from ben47 I am prepared for battle.