Thank you. Landy is 1987 Ex military 110. Retro fitted with 300tdi, LT230 1:14 transfer box and LT77 gearbox. There is a metallic tapping noise coming from underneath. Does it in all gears but only when trundling along and feathering the throttle. Sound is rhythmic and does not really speed up with truck only gets louder. You can feel the tapping 50mph to 70mph. Only does it whilst driving. Sound is difficult to trace. Sounds like rattling jaw faces together of two 19mm spanners. Replaced transfer box front output bearing, tapping still there. Removed front prop and ran it in diff lock, sound was gone, so bought a new front prop and sound returned. Anyone any idea whether is front diff or transfer box? Changed oil in all gearboxes and diffs and found nothing conclusive in the oil.