Just to confirm that I understand...
so normally you had your T100 running in 2H without any noises, then put it into 4H for a while. Now when you put it back into 2H there is a grinding noise but if you put it back into 4H it is quiet again?
Does it make a difference in 2H whether you are driving straight or turning a bit then?
Inital thought is that it is not coming out of 4H completely.... hmm
I wonder if when you put it back into 2H you can try creeping ahead slowly turning right and then left or maybe even trying this in reverse turning left and then right a bit. See if that makes any difference in 2H.
Certain that others with this particular drivetrain can offer specific experience.