Why does the Alarm sound shortly after doors have been locked using remote key. on 1998 Mercedes-Benz ML320

Rookie cbe0621eac06868b3efe0d8d1d3611e23c60d3114864ea2ec19a68cfbd3eebab
This problem has started just recently and it now occurs every time the car is locked. I have tried using differnt remote keys to lock the vehicle but the alarm is set off each time.
(1) Answer
(2) Comments
You were correct. My rear passenger door lock has a faulty switch. Thank you for your help.