I have a weird faint noise after the car is turned off like a humming

[Camvill]

any ideas what is going on? its not the fuel pump because i hear that turn off. its near the rear end

[The Fixer]

Pressure in the gas tank maybe? Try loosening the gas cap and see if you get a "woosh" of air, and the noise stops.

[Camvill]

i guess im just paranoid lol