pressure release

I've got a 2001 z71 and when I turn off the engine there is a pressure release sound coming from the engine, does anybody Know what that is?

do you have ac? thats probably all it is

I do have a/c but I havn't used it in months, if that matters.

It's your air intake. When you turn off most fuel injected trucks, you will hear a "last gasp of air" coming from the air intake. You can really hear it if you have an aftermarket Air Intake. If you figure out that is where the sound is coming from.... it's normal. :o)