check this thread too:
Ticking noise coming from right behind my left shoulder
Or quite simply, it could be loose change (stuck in your center console) if you or previous owner kept/keep change in your ashtray. The Boxster cabin is small so it's hard to always accurately tell where sounds are truly originating. with the car off, try rapping moderately on the side of the center console. If you hear the loose change sound then, you most likely have some coinage stuck in there. Search for center console removal or short shifter install on how to take out/raise the center console to dislodge.
Good luck
