I do not have access to information about your vehicle.
Before you start snatching your carpet out.
Maybe this would help you locate the sound
You said "or just for a few pumps after the engine has stopped."
This might be helpful, as with the engine running, it might be hard to hear it.
Can you get the vehicle up on to a LIFT/ JACK STANDS/ OR EVEN STRADDLE A DITCH (as I have a million times in my Jeeps!)?
Have your buddy crank it up, then turn it off. Crawl under near the gear shift lever. Have him actuate the brake pedal when you are in position.
You might have to do this process a few times to hopefully locate the source of the hiss.
Maybe the noise is underneath?
Insure your helper knows exactly what to do, no need in moving the car!
BE SAFE! BE SAFE!
The Medic
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Thursday, April 27th, 2017 AT 4:36 PM