93 RRC Transmission whine 60-65mph whats the cause

Having removed my front propshaft due to a seized viscous coupling I have now acquired a transmission whine (as well as being able to turn circles)

It is only noticable at speed at about 60-65mph when accelerating or crusing it is evident however when i come off acceleration the noise goes away.

As the front props off itmust be transfer box, propshaft rear diff or something else in the drivetrain.

Anyone got any ideas of where to start looking?

Thanks

had this on aclassic and found it to be the first motion shaft bearing in g box