locks

Unfortunately, the noise is inherent in the system: the lock motors are noisy themselves (not the motor itself but rather a disengaging mechanism inside), the rods and latches attached add to this, and the whole is vastly increased by the hollow door construction.

If you have the original remote control fitted, the passenger's side door lock does not activate the central locking by default: the central unit has only two triggering inputs, so Citroën had to use the second one either for that door or for the remote control.