So about 10-15 seconds after I shut off the truck this sound comes from the engine compartment in roughly this location and the sound has been occurring for several months now. Just over 100,000 miles on the truck





Something that may or may not be relevant is that I sometimes get a "small EVAP leak code" which is typically related to the fuel filler cap not sealing quite right, but recently have been getting a "very small leak" code and have no idea where it is coming from...