Earlier today I tossed it into 4-wheel drive high today and the noise disappeared. Does this confirm that its u-joints?

Also, it doesn't want to release from 4x4 mode. I've engaged and disengaged it using the floor shifter, and even put it in low 4x4 and back in order to try and get it to release. Its like the transfer case is back to normal but the differental is still locked. Any thoughts on this?

The truck just clicked over to 90,000 miles tonight.

The easiest way to check he u joint is to cut your wheels hard to the right(for drivers side, opposite for passenger) stick a large screwdriver between the joint and the yoke and pry bar and forth to see if it has any play or slack in it. My truck just rolled over 130,000 and I've replaced the drivers side twice and the passenger side once. Hope you get it figured out.

I jacked it up today and got a close look. I don't have any play in the u-joint, but there's a tell-tale sign - I have rust-colored dust coming off the u-joint. So the "grease-less" u-joint appears that it needs grease. So I'll be planning to replace them.

Also, got the front end freed up from the 4x4 mode. Rocking the tire back and forth checking the u-joint got it loosened up.
:U:

it sounds like u-joints for sure. when you put it in 4-wheel drive it stopped. now it feels like its still in but its not. the u-joint is binding up. my 04 did the same thing. replace u-joints & i bet it will show that transfer case is disengauging.

Thanks, makes sense.
:c:

Second on the U-joints