OD Lockup Clunk Noise When Starting Out?

2005 Grand Caravan with 3.8L. Less than 7K miles on car. There is a slight clunk – clunk noise from the front end when starting to move forward. It ONLY HAPPENS after the automatic transmission has been in OD & Lockup at speeds greater than 45mph and then after car gently brakes to a full stop. When I next gently accelerate there will be a slight double clunk noise from the front end within the first couple of feet of forward motion. It even happens if I keep the brakes applied and gently tap the accelerator after coming to a full stop. It DOES NOT happen when the car has been driven in 3rd gear (no OD & lockup) but the speeds and other conditions are identical. I am hoping that there is a transmission guru here who can tell me what I am hearing is normal. The car runs perfectly and has never had a fault code. If it were a motor/trans mount I would think that having the transmission in OD & lockup would not be necessary. The noise never happens if the gear selector is in 3rd gear or when driving at less than 45mph. The car is still under warranty but there is a deductible.