As others have said, the single beep is to let you know that something is open and the car may not be 100% secure. I got caught out with the oddments tray not being shut properly.
In the first couple of weeks of owning my 986, I kept getting this single beep and couldn't work out why my rear boot was always off the catch. I thought I had a faulty boot catch but it turned out I was using the wrong button on the key fob to unlock the car..
