Weird Alarm Problem

[MAC_600]

I've got a 97 GS 300 Mk1 Sport and don't really use it much these days.

As a result I often leave it in the garage with the bonnet up with it connected to a trickle charger. Recently an alarm has been going off, though not the actual car alarm. Its a sort of quiet siren sound coming from the offside front wing and stops as soon as the ignition is switched on but starts again as soon as it's switched off.

The alarm doesn't seem to have anything to do with the cars security alarm, as the car will lock and unlock via the fob but this makes no difference to this other alarm. I'm wondering if there is some sort of bonnet sensor and this is a warning to say that the bonnet is open. In the past I've taken the car for a quick spin and after a few miles the alarm has stopped for good, I've assumed it's some sensor that is stuck and the pothole roads round here bounce it back in to position.

Has anyone got any ideas as to what the actual problem is as the car is currently not taxed and everytime I do anything in the garage this alarm is driving me up the walls.

Thanks

Mac