Vibrations, sound of something running near Gas tank

So my mom asked me to figure out a sound she has been hearing.

This is when the truck has been off for several hours she will go to her truck in the morning on the way to work, before it is even started she hears a humming, vibration, near the gas tank. She can feel it when she touches the gas lid and can hear it from across the garage.

Any ideas on what it is? I feel like nothing should be running since the truck hasn't been started in about 12 hours. She says it happens almost every day.

 

It's in the owners manual. It's an evap purge that runs after a few hours of sitting. Totally normal, it freaked me out the first time I heard it too.

 

yup. evap kicks on by itself to keep system purged

 

awesome thanks guys.
I never noticed it on my truck so figured there was something up with hers but guess not.

 

Hummm never heard it after it has been off for a while but hear it alot when I turn off the engine almost every time:}

Is that normal as well ?

 

First time I heard it was in my FR-S and it freaked me out. Found out what it was and noticed both do it from time to time. Completely normal.

 

Someone JUST posted they thought their fuel pump was running......

 

tacomas also fart