2006 Lincoln LT 5.4 When I shut down the engine I with the hood up I get out and hear a hissing sound coming from the passenger side of the motor, I have checked all the plugs and they are all tight. Anyone have any idea what it might be??? THANKS Dallas

 

Is it a constant hissing or is it a short hiss after it shuts off?

If it's a short hiss, it is normal. All my vehicles do this.