Electric Motor Sounding Noise

Went into the garage to take a package out the back of my truck and I noticed what sounds like an electric motor humming. It's not a loud noise. It is coming from the fuel tank area.
Never noticed it before so just curious if anyone has noticed the same thing.

 

I started up the truck and turned it off. The sound is now gone. Just strange. Does anyone know what it is?

 

Old thread back to life. Same thing on my 2015 with 39,000 miles. Never heard it before.
Searched TW and got 4 threads on this. Apparently some sort of electric motor that vents or recirculates vapors from fuel tank? Part of emissions controls. Kicks in about 3 hours after engine shut down when everything cools. Got in and turned key to On, then off and it stopped. Dealer might have given a heads up. Weird unexpected sounds from a parked truck are generally a sign of demonic possession . . .

 

It's part of the emission system. It's the evap charcoal canister. Since we have a returnless fuel system it has to purge the fuel vapors and pressure.

 

Cool....