Dear Folks,
Finally, I catch the culprit, the sound is coming from "Throw out Bearing" (TOB) which needs replacement but UNIMOG can live with it. However, it needs minor clutch adjustment.
Drained entire Gear Oil, noting found in it. Internally, no damaged made to the gear/s.
I thank you all, who have participated in resolution.
UNIMOG REGARDS,:*
Abdul