We have this same issue. My wife and I Ubered 55 miles to the dealer last night to pick up our new Limited 4x4 Hemi eTourque. Driving away with huge smiles and still in the parking lot, we got our BT connected...and the rattle started. This resulted in us immediately turning around and going back inside the dealership. Unfortunately, we had to drive it away and now have to make arrangements to go back and forth for it to be fixed. I read on some other similar threads that some have had no resolution. I don't want the truck if it is going to rattle when we play music...we ALWAYS play music. Neither of our F150s had this issue even after upgrading their stereo to powerful aftermarket.
The two primary rattles that we immediately identified were with the rear sliding glass and the rear doors. If we pressed on the window, it stops. I'm not sure how the door pocket will be fixed as it is simple too flexible to handle the stereo. Perhaps adding those foam cup holders from the front doors would give it enough support, but will reduce its functional purpose.
This is NOT what we expected when I picked up my new $68k truck and I am worried that my plan to drive this the next 6 years will encounter more rattles. Any rattle for me is intolerable. As requested above, I am PM'ing Ram support.