I have noticed that you can turn the car off, then open the door too quickly and it will beep at you. I think it is because while the steering wheel retracts and moves up, the car is in accessory mode and the beep is reminding you. If you close the door and wait a second, the beep will stop and you can exit normally.
When I turn the car off, I wait while the steering wheel adjusts, and then I open the door and get out. Generally, I occupy myself by turning off Slacker Radio after I turn off the car, rather than before.