This annoying hissing noise happens between 1500 - 2000 rpms when the engine is revving down. I have brought the car to 2 different dealerships for this problem and neither of them know what they are dealing with, but they tell me its not a problem because the check engine light isnt coming on. There was a thread i had followed for a while, but im not sure its the same thing. http://www.audizine.com/forum/showthread.php?t=160948 I took a stethoscope and poked all around the engine and heard nothing. then i took it to the exhaust system and it was loud and clear. someone mentioned that it might be a pressure flap in the exhaust making the noise. i dont know what to do. Every response is appreciated. Thanks