Renault Megane Dynamique 1.4 05 model alarm sounding when card is started?

The alarm system on the vehicle seems to be doing curious things. When starting the car there is a 50% chance the alarm will start sounding and all external and dash lights flash. When this happens and the car is switched off the alarm sounds fades away but the lights continue flashing and there is a clicking noise from the boot on the near side. I have removed the inner covering of the boot and there is an led flashing and what I assume is the alarm unit. Ther lights will continue to flash and after 10 mins or so will stop. The car never fails to start and can be driver even with the alarm sounding (which is rather embarrassing). Before I book this into a garage I was just wondering if anyone had come across this problem.