something running after shutdown

Occasionally, after parking the 2016 4Runner, I come back to hear a very faint noise like some kind of electric motor running. The noise is strongest by the left rear tire. If I turn the ignition on and then back off (without cranking), the noise stops. Any ideas what this could be?
Thanks.

 

Evap system pressure test or something like that. The newer toyotas do that.

 

Thanks. I was wondering if it needed to go to the dealer.

 

This is mentioned in your owner's manual, on or around page 8 (mine is a 2019, and that is the page this information was found.)

 

yeah...first vehicle we had that did that was our '14 Sienna. Drove me nuts for about a week. then I read the owners manual

 

Thanks to all. I got the manual out today and found it. There's too much stuff in the owners manual! My wife got a 2019 Kia Sorrento and the three owners manuals take up most of the glove box! Her manual has over 40 pages on the airbags.

 

My 2006 Tacoma does the same. An air pump is purging volatilized gasoline from the headspace in the fuel tank through a carbon filter. Be careful "topping off" your gas tank because it can damage the system.