Hey Mario, welcome to CB!
Could be what Tim said. The CV part of the driveshaft (double cardan joint at the transfer case) can make weird noises when they start to wear. Especially the centering ball section. There are 3 grease fittings on one of those. One each at the joints, and one female type in the center. So add some grease anyway, just to see if it changes.
Unfortunately, u-joints don't usually make that metal-on-metal sound, but you never know.
Check your rear pinion yoke just to see if it's loose. Quite a few have had that happen here over the years.
Could be internal to the rear end, also as mentioned. Even wheel bearings, though like the u-joint, this is farther down the list of possibilities.
What does the t-case shift like? Does the sound go away or change at all when in 4 wheel drive? You can leave the hubs unlocked and put it in 4hi and low without hurting anything. Give it a try and see what the sound does, if anything.
Is it a manual transmission, or automatic?
There are plenty of bearings in the boxes there, but did the shop happen to check the bearing in the intermediate housing between the t-case and the trans? Was the shop a gear expert? What exactly did they do to the t-case? Did they pull it out of the truck and open it up on the bench?
Did the noise just start out of the blue, or did it start gradually? Or was it always there since you bought it?
Just a few more questions! ;D
Good luck.
Paul
