im far from qualified to give advice but if its worse in low range i would check the fluid levels of the transfer box first. also wouldn't harm to check the gearbox and diff fluids the same time. when i had mine it had a very slight wine over 60, changed all the fluids now i can barely hear a wine unless im traveling at about 70mph cause its naughty to go over that hehe.
also stopped it complaining when im towing more than i should weight wise (that part is legal its always off road and to clarify too much weight its a 3.5ton fully kitted ambulance normally up a grass bank or muddy field lol)