Is your driveline a two piece set-up?
Does it have a center support bearing(carrier bearing)?
Also like Bill mentioned, it could be the clutch plate installed backwards (clutch plate rubbing against the flywheel)
Does the noise occur while moving or sitting still?
Is the noise constant?
What rig is this you are working on?

There is enough good in the worst of us and enough bad in the best of us that it does not behoove any of us to criticize the rest of us.
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Be yourself. If you are ever lost, It will be much easier to find yourself if you know who you are!