Just went through this a few weeks ago with a different forum member. His front diff seal was bad and drained it dry... IMO start there. Drain/check fluid for chunks/shavings/level in both the trans and front diff. Refill and see if noise goes away. After that it could be the support bearing on the driveshaft that's above the skidplate (kinda centered in machine) check/grease that... after those items it's most likely internal parts of the trans/diff.....
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