This is probably normal, but on occasion when I turn off my 2005 SL600, I hear a rather loud ticking noise coming from the car, other times when I turn off the car I don't hear any ticking noise. Anyone have any ideas???

I can't tell for sure where it is from, appears to be either under the car or in the engine compartment area.

Metal expansion due to heat. It's normal.

It's one of the joys of my F355, sitting in the garage after a spirited run, listening to the ticking as the engine cools down. Almost certainly comes from two jointed metal parts cooling and contracting at different rates and a tick happens when one part slips against the other. A mini San Andreas fault if you like. Completely normal.

I expect the ticking is related to how hard you've been exercising those turbos...