Humming noise on the undercarriage of the back of the Truck

Last night I was in the garage and heard a humming noise coming from underneath the backside of the bed of my truck. I called my local dealership and talked to a Service Tech who told me that is normal, its your emissions purging. He told me that you can only hear it if it's in a garage. My truck had been in the garage for 4 hours. Has anyone else heard of this?

 

yup, its even in the manual. Thinks it states aprox 5hrs after turning the vehicle off. had my neighbour knock on the door to tell me he heard this, and I looked it up thinking something was wrong, had been in about 5hr after I parked. Perfectly normal operation, I checked my manual that evening.

 

Thanks, it freaked the hell out of me!

 

Yup normal.

Its a pump that runs to do an emissions / evap pressure test of the tank and respective systems. Its why a code gets thrown if you leave your gascap loose.

 

Noise from under vehicle after turning off the engine

Approximately five hours after the engine is turned off, you may hear sound
coming from under the vehicle for several minutes. This is the sound of a fuel
evaporation leakage check and, it does not indicate a malfunction.

is directly from the owners manual.

 

It's girls given your truck a Blow Job.

 

Does this occur in all 2nd gens?