drivetrain issue

[m5sjs]

hi i have a 2003 x5,i think i have a drivetrain problem,when i am driving in traffic ie stopping and starting there seems to be a split second when i press the throttle until the power hits the ground, also when this happens there is a dull thud noise coming from under the car mybe from the middle to front area,also when i select reverse gear there is a click or clunk noise which i don't think should be there,i have replaced the rear subframe bushes so that is not the problem,i put the car on the ramp to see anything obvious,i noticed that the output shaft from the transfercase that connects to the front diff shaft there seems to be play from the connection between the two,is that normal,mybe someone could let me know a problem area to look at,i hope i have made sense,thanks for your help,