Two problems that may be related, slight shuttering in rear wheels when accelerated, starting issue

New 2019 all wheel drive Ford Flex. The first time I turned right when I drove it off the lot there was a slight shuttering in the rear of the car coming from the wheels as I accelerated. Was this normal? It only happened when starting off while turning right or left.
At about 475 miles I began having trouble starting the engine. The engine would not turn over when the start button was pushed (with my foot on the brake.). The display indicated the car needed to be taken out of the accessory mode. So I pushed the start button again without my foot on the brake and it turned off the accessory mode. Then with my foot on the brake, I pushed the start button again. The engine sounded like it wanted to turn over for an instant but reverted back to the accessory mode. I repeated the above procedure 5 or 6 times before the engine finally turned over and started. Then everything seemed okay, except for the shuttering described above.
At 480 miles I took the car out to the dealer and had the salesman witness the starting problem and also the shuttering as we drove it in their lot. We talked with the service manager who set up an appointment at the end of the month.
So I went home.
The next day I had to drive about 35 miles to an appointment and when I left home, I had the same problem starting the car as stated above. It happened again after my appointment. When the car finally started I backed out of the parking space and turned to drive out of the parking lot. More rear end shuttering. I turned right into the road, accelerated and there was a loud bang in the rear of the car. I took my foot off the gas and rolled to a stop at a traffic light.
when I looked at the display the engine light had come on and there was a wrench displayed in the message window. There was ford dealer on the other side of the intersection so I gently put my foot on the gas and there was another bang with some hesitation as my car moved forward. So I turned into the dealer's lot and went straight to the service write up area. It was going to be the following week before they could look at it and told me I could leave it but they couldn't drive me home because I lived beyond there shuttle service. So I said I would take it to the dealership where I purchased it, 40 miles away. I experienced 3 more very loud banging noises as I turned back into the road with in a few hundred yards so I turned around and took it back to the Service area. It's still there. The report from the dealer is that the battery had a dead cell which caused the starting problem, the installed a new one, road tested the car for 22 miles and can't recreate the problems in the rear of the car. Everything is fine.
Well I would like to know what caused the bangs. Is there something electronic going on in the all wheel drive system that could have been related to a bad battery? How does the all wheel drive system work?
Am I going to driving a problem likely to fail again on some dark highway, out in the country, in the middle of the night?