Spoon Sports 12/5/2011make sure the vacuum hose on the fuel pressure regulator is on, on the bottom of the fuel pressure regulator on the fuel rail, its a small black vacuum line that hooks to the nipple of the regulator. OR it might be the refrigerant (A/C) pressurizing or something. My MCS does not do this, but my other vehicles do this after driving w/ the A/C on. The hotter the day, the longer it "hisses" for.
Try running w/o the A/C on (even better w/ the whole auto a/c system shut down), and see if your car hisses at you after a drive.
I might be the supercharger, i blieve the S has one equiped. Whether it's somehow depressurizing or coasting to a stop, you can hear it because the engine is off.
By the way, welcome to the club, you are not alone
Spoon Sports 12/13/2011Sure thign chief.