No noise with the truck in the air. So no load on wheels or suspension. What changes that could make that noise?

There would also be less or very little load on the powertrain but you could put a load on it while up on stands by applying the brakes.

Try pulling the rear drive shaft and driving in front wheel drive.

It's going to be a process of elimination. Done for free by yourself or by a shop you have to pay for.

 

this ^^^

and pull the boot over the gearbox, so you can hear the noise from inside the compartment better.

with the boot off, you could use a mechanics stethoscope on the gearbox, to see if you hear the noise coming from there, while you are driving, $3.99 at harbor freight:

http://www.harborfreight.com/catalog...?q=stethoscope

that will help eliminate the gearbox, at the minimum.

 

I found the problem. it was a seized front passenger brake caliper!!
But now my rear pinion seal is leaking diff fluid everywhere and i have a horrible rumble at high speeds.......... time for a diff rebuild. the question is....re-gear or locker......