I have a hissing sound while motor is running with or without the a/c running. When car shuts off you can hear it wind down psst. Anyone have any suggestions. Car seems to run fun - just unusual noise.

 

Possibly vacuum leak?

 

Gotta be a vacuum leak.

 

Had same thing. Found small diameter vacuum hose going to a small canister on driver sidewall of engine bay. Had crack on bottom. Wiggle the hoses around that area with engine running and you'll find it. I just trimmed the hose and reinstalled it. Problem solved. (As always, be carefull in the engine bay with engine running).