When I shut off the engine of my 2007 GT/CS there is a sound that com,es from the engine copartment that lasts about 1 second. It sounds like escaping gas but I can't figure out where it is coming from and why it happens. Has anyone experienced this? Everything else is normal. It's like a burp after shut down. Hmmm.

 

I've had escaping gases but coming from another area

On a serious note: I bet it's coming from your intake if you have a CAI. I used to get the same noise on another car I had with a CAI after shutting the engine off...

 

The sound is completely normal.. nothing to be worried about there.

it's basically compressed air coming back out through an intake valve that didn't close as you switched off your engine.
you'd hear the sound more if you upgrade your closed filter box to a Cold air intake.