Door Locks 93 300D 2.5

After locking my doors with the key all four lock knobs pop open on there own after about 45-60 sec. I can hear a wirring sound comming from the back seat. I am assuming I have a vacuum leak somewhere or a malfunctioned pump under the back seat. Could the door vacuum actuators be faulty? I am trying to keep this simple at first before I need to take the door panels off. Thanks for your help Mike Stillwater, Minnesota