Help diagnose the noise! Defender TDI 300

Loud clunk going down the motorway as if someone was hitting the chassis with a hammer.

Had full front axle apart, even replaced front diff, exact same sound.. prop shaft is all good, drained transfer box all clean oil, removed transfer box inspection cover everything is tight and clean.

When front prop is removed or vehicle is in neutral there is no sound. Please help it’s like a bag of spanner’s!

Any help appreciated, thanks

Have you taken the side/inspection plate off the transfer box?
Any play in the input/out out bearings?

When you had the front prop off, did you turn the diff input? I'd be trying to isolate the sound, whether it's in the diff/axle or in the transfer/main gearbox .. or even clutch/flywheel.

Maybe a CV joint has failed. Messy to check, but it's where I'd look next.

I have not removed the side casing on transfer yet... will try tomorrow. No play in the output when prop shaft was off.

All halfshafts are good.. defiantly not anything to do with the front axle as I first thought.

It must be something from transfer/gearbox/clutch

When you put into neutral did you take foot of the clutch?
If you put it diff lock spin the back wheel to turn the gear box & listen for noises

I guess it does it with the wheels on under normal driving conditions?

The transmission can make evil noises if its not actually driving anything

Try running with diff lock in, [rear wheels off the ground] If it then goes quiet this points to a center diff problem.

Yeah I drove 100 miles like this on the motorway. It happened on the way to the Land Rover show so had to make a U Turn!

When in diff lock and front prop removed there is no noise, this only happens when front prop is fitted and under load. It’s louder the higher up the gears you go...

Removed transfer box this evening... no noticeable damage in there all gears, bearings are good with no play, no metal or signs of damage! The only thing I can’t see Inside is the centre diff?

Can you start it & see if the noise is stilll there? This will eliminate transfer/axles/props

Center diff comes out the front.