This is a common fault it is the battery backup device called an alarm sounder it has its own internal battery's and when they no longer hold charge go off at random usually in the most embarrassing places? sound familiar? for pictures of how to remove try here great place! www.fronteraowners.co.uk search for alarm sounder! hope this helps as I had same problem on my 3.2 51 plate!
Mufftrix, November 2007