I have a 2001 GTP Coupe with 110K, and was diagnosing a water pump problem the other day when I noticed after I cut the engine off, there was a hissing noise coming from the driver side/rear engine compartment for about 30 seconds. I duplicated it several times, played with the obvious vacuum hoses, but could not locate the source. There doesn't seem to be any performance problems that I can't attribute to my water pump going bad. I'm not too heavy on the car, learning as I go, does anybody have an idea where this is coming from? Is it a normal pressure release or should I be looking for a vacuum leak? Any ideas would be appreciated.
