Heelo ammar, it was my first day with GS-150, and to put it simply, I'm convinced the 'khattak' sound comes when try to put the bike in 1st gear while the idling rpm is considerably higher, more than 1500, usuallt around 2000 rpm.
if the rpm are stable at 1500, i observed no sound.
you have a right to disagree though :-p