Well the same click sound occurs in City AT (5th gen). Either from P to D or N to D.
If i am not wrong, the click comes about 1 sec after D engagement. Poster can confirm this.
Xulfiqar sir, I believe (rather I have felt that) the parking pin disengages right after shifter disengages from P. And the click sound is like some sort of clutch engagement.
Self EDIT: Correction. Just rechecked this morning. The click sound only comes when shifting from P to D or R to D. Nothing happens when going from N to D.