Driving my 2000 powerstroke home from the local dealership after a recall today i noticed when i let off of the throttle that i would here a whoosh sound. I called the dealer and they said that they never heard it do that when they drove it and couldnt give me an answer. They were working around the driver side of the vehicle in the wiring harness to do with the cruise. My pickup has never made that sound before....any ideas on what it could be? I am possitive that it just started on today sometime between when i dropped it off and started driving it home. I need to haul big load with it saturday and it will be a good 4 hour trip so any help would be deeply appreciated.

Thanks