Winding down noise

I have a 98 Windstar. When I shutdown the engine I can very faintly hear a sound coming from the engine compartment like something spinning and winding down like a propeller coming to a halt. Any ideas? How serious?

Thanks

If the engine is warm or you have the Defroster or A/C on the radiator fan will be runing, the sound is normal. Do not worry about it.

Thanks,
I check that out later.

I think I've heard it said that the trans turbine can make that kind of noise and is ok.