dont know if on your year your horn should sound with the locking of vehicle, but if it should you should lock it using plip and keep pressing plip button again and again it might beep horn. (helps find car in car park)
if it doesnt beep and it should then its possibly contacts under airbag, but also could be horn itself. need someone to press horn with ignition on whilst earth and live present on horn unit. horn unit found under plastic shield underneath headlamp on passanger side.
me
November 2009