Land Rover Repair: TD5 vibration when slowing down, transfer case, standstill

Question
I have a 2002 TD5 manual discovery.When i am slowing down with the clutch depressed, the vehicle makes a rotational clonking noise that can be felt through the car as it gets to about 10mph.It only does it with the clutch depressed and or in neutral but if slowing down while in gear,no noise is heard.I have switched off the engine and the noise  is still there until the car virtually comes to a standstill.I have found that if i knock the high /low stick into neutral, the noise disappears.The car drives perfectly at all other speeds and there is no indication of any other fault.I have checked both propshaft joints and sliders.Do you think the problem lies with the transfer box. Any advice would be much appreciated.

Answer
I would remove the transmission/transfer case as a unit and examine them and the clutch.  The cause of the problem will probably be visible.

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John Elder Robison