So, to attempt to summarize:
-Thumping noise remains constant, does not change with speed, braking, road surface (not impacted by bumps/potholes)
-Appears to be coming from the driver's side wheel
-Can feel something in the floor of the truck corresponding to the sound
-Do not feel the thumping in the steering wheel
Additional questions:
-Does it seem to be front or rear wheel area?
-Is the noise still present at idle when the vehicle is stopped?
Is that pretty much accurate? That's very odd, it can't really be related to engine, drivetrain, wheels, tires, brakes if it doesn't change proportionally to the vehicle speed or the engine speed. This would pretty much indicate the noise is a relay, electric motor, or something in the radio/speakers.
Does the noise change if you turn off the blower motor, HVAC system, and radio?
-Rod