62TE 2012 Caravan trans thunk

Wifes new(ish) minivan has a clunk when going to D or R, and occasionally on the downshift into 1st when coming to a light. Does it in "Econ" and normal shift mode. Feels sort of like if your U-joint/CV joints were bad and the driveshaft was taking up the slop. Someone mentioned an "underdrive compounder" that was serviceable "in the car" with access panel behind wheel? G. Caravan has 51K on it. Ironic that a rental place would unload it at the end of its factory warranty period? It doesnt bother her but I cant stand it, her 2002 dropped into gear just fine, and my 24 year old Lexus wont even let you feel it when you drop it into gear. WTF?

don't you have a 5yr 100K mile powertrain warranty? get it serviced.