What is this?

This particular piece is mounted on the subframe underneath the bed above the tank and measures about 12" x 6" x2" and had an electrical type cable connection.

Once in a while I go out to the garage and can hear a "humming" noise coming from it and when I grasp the cable there is a change in pitch and tone so it is definitely the piece that's making the noise. Sometimes I hear it after 6-8 hours of the truck running, but only like once a week.

I "clear it" by turning on the ignition then turning it back off and the humming stops.

Any clues?

TIA

 

It is part of your emission control system. It is normal. No need to reset it. It is purging evaporating fuel from your fuel system.