Clunking noise from front end of Isuzu Rodeo 2000 only in 4x drive.?

If the axle shaft boot is torn, the axle shaft is most likely bad. Actually it's the cv joint that goes bad, but to replace a cv joint the axle shaft needs to be removed. It's easier to replace the complete axle shaft, as this saves time. This can be checked the same way you'd check a driveshaft for a bad u-joint. Locate the center of the axle shaft and try to rotate it. It will have some end to end play, but not rotational. Most axle shafts cost around 125-150bucks and have a core deposit. Hope this helps. Christopher