I have same year as yours but a 2 litre diesel. My bonnet doesn't lock all the way down either and I have tried altering the rubbers that you see under the bonnet, but to no avail. There is no vibrations coming from it and also it is locked fully so no problems with the bonnet coming up when you're on the motorway. I've just lived with it and not really gave it another thought.
Blue 2 Litre Diesel Ghia ,2005, Front and rear parking sensors,fridge, sony 6 cd player, Full cream leather interior.Favourite of all-sunroof for those hot British summers