just bought a 97 ford f150 with a 4.2 motor. auto trans. 2 wheel drive. i have a vacuum leak located somewhere on the passenger side somewhere behind the pcv valve. when i shut the truck off i hear a hissing and then a whining noise. i can't really see where it is coming from. i'm 62 so climbing around a truck for long periods of time is an issue..can anyone give me an idea of what the issue is.