Originally Posted by TexEdition

That intake sound after you kill the engine isn't from sucking air IN. How could it? It's "unused" air escaping from the intake.

And yeah, if you've been running the a/c you'll have a hissing for a few seconds after you shut down..

Originally Posted by Bent6

It's not sucking air in. It's atmoshpheric pressure rushing into the low pressure inside the intake until the pressure equalizes.