Central locking fault - 2008 facelift Style 1.6

[stevetuk]

Hi, first post so very much a newbie. Am looking for some help on this one.
Took my 1.6 2008 facelift Style into the dealership to look at part-ex for upgrade and they said there was a fault with the central locking.

On the second press of the keyfob to lock the car, there is a high pitched squealing/whirring sound. I thought it was normal as it was there when I bought it but apparently not.

Have tested it out at home and pinned it down to the rear driver-side passenger door.

Does anyone know how this can be fixed and what the costs are likely to be? Is this a known fault? I had the car serviced twice by the same dealer (Nov 2010 and Nov 2011) and it was never mentioned. How long does it take for the fault to develop the sound as a symptom? Should the dealer have picked it up?

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