99 powerstroke whiseling/hissing air noise
 

I have a 99 powerstroke making a weird whisel/hissing air sound coming from top of motor by fire wall. Don't do it unless you are going steddy speed down the road gets boggy/slugish when it dose it. Almost sounds like bad boost leak out side the truck. Looking for info on what it might be its loud and gets old lol

Could be a loose clamp on the turbo that goes to over to your intercooler would be my guess.

Could be your exhaust back pressure valve...