Weak or no door locking sound

[taylormj4]

Ocassionally recently, when I go to lock the car, the usual "thunk" locking noise is either rather weak or non existent. The car appears to be locked nonetheless (door buttons do not open the door) but there is obviously something developing.
If I unlock and relock, the usual "thunk" returns.

Anyone know if this is likely to be an immoboliser, door solenoid or wiring problem from similar experience ?

PS It's not low battery as the car starts and drives fine and is used daily.

Thanks.

[Chimjunkie]

Sounds like the locking mechanism may need some lubrication and the solenoid is struggling to move it. If it is shagged let me know as i am breaking my chim for parts.