loud bang when braking in 4x4 high

[BubbaRand]

Cannot find why 4x4 high started making bad noises - an now up on stands and when put in drive then, even with gas pedal not pressed, and pulled into 4x4 high - front wheels turned but when brakes applied I get scary loud bang in front (diff I think - hard to tell). Sounds like a LOT of backlash type of sound when brakes quickly slow or stop wheels from turning. How do I determine what the problem is? Really need help with this one - PLEASE!

 

[LibertyTC]

What Year is your jeep?
It may be best to diagnose with Jeep on the ground, not on stands.

 

[KJowner]

Have a feel around the joints to see if anything has lots of backlash.
I'd pull the diff pan off as well.

 

[ltd02]

Wiggle the front prop shaft and both half shafts. Are all the boots ok?