1997 4x4 problem

When engage 4HI the car has a rumble then when I shift back into 2 wheel drive, there is a really loud clunk. I don't have any clue what is wrong. If someone could help me out it would be great. If it is going to cost more than $800 to fix we want to go ahead and sell it. It has 127,000 miles on it. Please Advise!!!

Before you sell, try to determine where the noise is coming from (or you might be giving someone a great deal). It sounds like it could just be a front driveshaft u-joint. But on the worst end , it cound be a front diff problem or something in the transfer case. but both of those are not common under normal use.