My 2004 VW Passat has an issue where the nearside rear door will not always open when the corresponding button is pressed on the car key. When the other doors are unlocked, the faulty door makes an unusual noise as if something is trying to move but can't. Apparently its quite common with VW cars of this age.

Has anyone had this problem? Does anyone know the most likely cause of this problem?

UPDATE

The rear nearside door now consistantly won't open, making replacing the door lock actuator (the part that is currently believed to be at fault) somewhat harder to replace.