Hissing sound: vacuum leak?

[Deuce]

I'm getting a hissing sound from behind the dashboard (sounds like somewhere behind the radio) when I accelerate. Starts off quiet but increases as I accelerate. It does stop when I the truck gets going and the boost lets off but then immediately starts again when I let off the gas and the rpms slow down to cruising rpm. There is no sound when traveling at low rpms (ie on the hwy or in town driving). It only occurs during acceration and deceleration. Sounds like a vacuum leak. Are there any vacuum lines coming in through the fire wall? It's definitly not the turbo because I can hear that spooling up as well (different sound). Any help would be appreciated.

 

[ticlone]

If you open up the part of the dash where heater/ac controls are and pull it out the module that has all of the heater/ac control vaccum hoses on it, may not be seat all the way in. Make sure that is good and snug!

 

[Phoon30]

Also there's a vac line running behind the passenger side dash speaker. Gotta take the speaker out to get to it. I can't remember if there's a conection there or it's just a line. It's been a while since I've been in there. Maybe something for ya to check in addition to what ticlone posted.

 

[Deuce]

Thanks, I'll check it out this weekend.