This is a tricky one because without the ability to hear the noise it’s difficult to say what the exact issue is, if it were me I would be getting it nice and hot, putting it up on a lift and camping out till I heard the noise so I could determine it’s origin. The most logical explanation is something with the exhaust but once again this is difficult without hearing the noise. That said this will most likely be under warranty so if it is more significant then it should be handled by the dealer.
I didn’t come up with anything when I searched for similar problems for this vehicle so keep us posted on your findings should you have any.