Noise when turning off car. wtf?

[Mikey Mustang]

'99 GT. Some times when I turn the car off after driving it makes like a "pffffff" sound like 10 times or so, sounds like its breathing lol what can this be?

 

[stallion98gt]

have u been using AC before ?

 

[crazystang05]

yea my 98 does that to its more kshhhhh i have not been using ac

 

[Mossberg]

normal