Hi!
Have a def 200tdi 110 with a DX Roverdrive to the LT77/LT230. When engaged it whines a lot. When you take off the foot of the accel pedal, the whine disappears.

In normal driving condition without the OD, the whine is not there. Any clue what is happening. Have check the everything on the OD. Do you think one of the bearings is gone on the OD.