I recently bought a 1999 996 convertible. The factory alarm seems to have a mind of its own. It chooses to go off when it is armed after 5-30 min. at least once. This is a problem when you are not around your car and can not turn it off because it beeps for 3 min or so. The alarm goes off w/ the top up or down. I have even armed it by pressing the alarm pad button 2 times so the motion sensor is not supposed to be activated. Does anyone have an idea of what this and finally is there any way to put the alarm in valet mode or something?