???Some sort of motor running while parked in the garage???

Got home from work yesterday around 6:30 and parked the truck in the garage. Shut the garage door and went inside with keys in hand. Went back out to the garage around 11:30 to grab something off the workbench and heard a strange "motor running" sound near my truck. Almost sounded like an electrical pump or something. Or like a cheap RC car motor at full speed. Sort of an electrical motor sound.
At first I thought is was something connected to the house; AC unit, bad electrical connection somewhere, buzzing electrical outlet, an alarm clock going off in an adjacent room... None of that. Walked all around the garage, house and outside too. Finally started listening around my truck. It was coming from somewhere near the bed. It actually sped/revved up for a second or two and then returned to the regular speed. I crawled under the tailgate near the spare tire. It was definitely coming from under the bed somewhere.
Of course then it just stopped, so that's as far as I got with my search. Anyone else encountered this?

 

Fuel pump? does it "whir"?

 

Its some emisions thing, scared lots of people on the forum lol. There are lots of posts about it.

 

It wasn't really a whirring sound. Sounded more like it had some pistons going in it. But not as heavy sounding as a small tire inflator/air compressor.
I guess it could be a fuel pump. But 5 hours after being parked?

 

Never heard that from mine while parked in the garage. I've only ever heard the fuel injectors "ticking" while cleaning them selves. Interesting...

 

Fuel evap leak check, per the owners manual...

 

I suppose I was half correct with the fuel system part lol

 

Well, there it is. And it was literally 5 hours on the nose when I heard it.
Thanks Beer:30

 

mine did that and i was looking all over my garage trying to figure out what it was then realized it was the truck. found out on this forum is normal since then maybe it has done it 2 times that i know of. does seem a bit strange that electrical components will turn on and off hours after shutting it off. guess this is the new normal..

 

I was out camping a couple weeks ago in the middle of the desert. Me and my friend were sitting around the fire and it was dead silent out and this shit started and scared the shit out of us at first. Now I know.

 

I have this shirt