Thats what I hear for about 5 sec. after shutting off truck,starts quiet then gets louder like someone is sHHHHH you in a theater or something.sounds like alittle backpressure to me, really didn't notice it till I had the hood open. yes I do have a 12" bigmouth on it so it is open. Normal?? EXTREME?? oil pusher??

 

mine is making that noise now too. I put a JL ram air setup on it and ever since I hear that too after shutoff.. I have a 92 Bronco that has done it since new......must be OK......JR

 

My truck does that to. I think it's got gas!

 

ever since i put an airaid on mine, it does it too.

 

Alot of F-150's do it. My cousin has a 97 F-150 w/ the 4.6 motor.......guess what his does it too. Mine has done it since day one. I heard somewhere it has something to do with a fuel pressure bleed off......or something

It is nothing to worry about.

--Joe

 

My 4.6 does it!
JJ

 

My 5.0 302 did too, only in the summer.

 

Mines does it when i turn the a/c off after the truck is turned off

 

The entire intake system is under a 22" vacuum when you kill the engine. Probably the source of the noise.

 

THANK YOU EVERYBODY one less thing to worry about,GOD I LOVE THIS PAGE

 

it's the vac pressure relieving itself from the s/c. You can hear it after installing those systems because it is open to the air rather than chanelled through the frame. Man can't believe that scared you guys... I nearly orgamsed when i heard that for the first time.... hehe just messing with you. It's good to be cautious

Mark