on the driver side door there is an instruction about the free wheel hub.
its written that to shift from 4H to 2H,the vehicle must be reversed about 2 meters after the hub is free.this is if the vehicle is using automatic free wheel hub.

my pajero is using the manual free wheel hub.
couple days ago,after using 4H i free the wheel hub and shift to 2H.i did not reverse the vehicle but continue driving forward.the vehicle did move but there is this loud knocking noise coming from the front.i stop, shift to reverse, and after reversing about 3 meters i drive forward again.
the noise is gone and the vehicle drive as usual.i hav never experienced this b4.
and the 4x4 hasnt been use for some time.

vehicle is a LO47GV Pajero,manual transmission,4g54 engine.everything standard.

my question are:
why must the vehicle be reverse for the specified distance?
mine is using manual free wheel hub,should i reverse each time after shifting?