o3 Blazer has developed a loud clunk/knock from the front end when placed in 4WD, the noise isn't constant like a u joint. But more random. Any ideas?

 

I see that I am two years late on an answer and I hope you've got it solved already. But I got alot of noise out of the front once due to a seized up actuator cable that would allow for a solid engage. I'd get a clunk out of the front differential when it disengaged and occasionally just a grind. Had to replaced the cable.