Our 2009 C30 recently developed an issue that's happening now on almost every drive. While driving, it sounds like the driver's door lock is engaging, then disengaging (lock...... unlock) over and over again every minute or so. It isn't constant - just happens enough while driving that it's getting irritating. It's very noticeable.

We've kept an eye on the physical lock post at the top of the interior of the door, and it does not move up or down when this is happening. Something inside the door mechanism is making this sound and I can't figure out what or why. The door locks (using the key fob) are operating normally.

This car does NOT have auto-locking doors, the kind that auto lock when you put it into gear. Appreciate any help as to what might be causing this