Transmission Noise?

You cannot say for sure without tear down -- meaning, removal of the transmission to access the clutch, pressure plate, bearing and so forth -- but it could be a broken clutch spring, for example, or other component in the area. This will take some time and money to be sure.

Couple of technicians - one in hoisted vehicle for operation + one underneath listening with well trained ear should be able to gather a pretty good idea of what / where the problem lies .. May require a 'drive on lift' with wheel jacks - which a well equipped shop will have. https://repairpal.com/repair-shops