Noise in motor when engine shuts off.
 

My friend has a 2008 Cayman S and all of a sudden when he shuts down his motor, it sounds like a marble is moving around someplace, then it stops. This happens every time he shuts off motor. Other than that the car runs fine like it always did. What could it be? Car has 50,000 on the clock, thank you.

That doesn't sound good, I would say IMS bearing, but after shutoff I don't think so.

I would grab a stethoscope and see if you can hear where it's coming from.

Is the motor completely shut down when the noise occurs? Mine spins for a very short bit after I turn the key. If it is completely done rotating, then it's likely a loose cat heat shield-of course that can be wrong, but I have had hear all kinds of strange noises from my CS on startup and shutdowns that go away the next week!