Why is my 2018 Audi Q5 showing an all-wheel-drive fault and shaking at idle?

A customer brought us a 2018 Audi Q5 Premium Plus with an AWD warning and idle shaking. There were two separate faults: a broken fork in the rear-differential clutch pack caused the AWD fault, and leaking hydraulic engine mounts caused the idle shaking. We replaced the rear differential and both mounts.