Whining Defender

Hi all my 300 tdi auto Defender has a whine only under load and worse around 40-50 mph I have changed rear diff with no effect, mechanic thinks it’s the transfer box but he does not seem certain, still sounds as though it’s at rear of vehicle any ideas or things to check please

I diagnosed some of my issues by getting the vehicle up on jackstands, running it and listening 'everywhere' ..

Wheel bearings

Unhappy kids in the back?

If it is whine it is likely to be transfer box or diffs. I have found wheel bearings an props tend to rumble when the are failing. It may be worth a quick check of the oil in the diffs an transfer box. Check its level, condition, and smell. If one of them is glittery with metal particles or smells burnt you have likely found your culprit.

Sorry for the delay, update so far rear diff changed, transfer box changed and she still whines under load, thinking its either front diff or auto gearbox, any ideas