When I switch-off my 04
MCS, I hear a what sounds like a "spinning-down" of a small propeller. It reminds me of the decending pitched-whine that the old TV Batmobile used to make (I'm dating myself, here) when it came to a stop.
My thought is that this my be the impeller of the supercharger spinning down. However in my 328i, a similar noise (though not in a descending pitch) is made by the stepper motors of the climate control.
Anyone know for sure what this is? I love the sound and grin ear-to-ear when I am reminided of the Batmobile. Holy Supercharger, Batman!
Theo