Front end whining then clunk

[something]

I think it's the front end....

 

Went on a 4X4 trip with my 95 Jimmy, went out of 4 wheel to hit pavement and go to town, on the way back to camp I heard a loud whining noise....slowed down and pulled over and before I could come to a complete stop there was a clunk noise, then all was fine.

 

6 months later exact same thing happened but had not used 4 wheel drive since the trip....again all seems fine but those two times it sure did not sound fine!.

 

Is this sounding familiar to anyone or know what it is?

 

Thanks