Global Mod Team
Join Date: Nov 2002
Location: Congleton - The centre of
It sounds VERY much like a door being left open. Since you have checked this and say it is not the case, my guess would be that you have a faulty sensor on one of the doors, so the alarm thinks that it has been left open.
If I had to guess, I'd say it's the boot, since the sensor used there is a daft, complicated, easily broken thing. Not sure how you'd go about checking this though.