Need drivetrain help

After helping a friend with his '92 Sport 4WD this weekend, I'm a little stumped:

He brought it over to have me look at it because it makes a loud metal-to-metal popping sound when turning left, and when you accelerate it "skips" like it's missing a tooth on a gear somewhere.

He took it to a shop and they told him he needed to have the front axle rebuilt. We removed the front driveshaft, but it still skips and makes the popping sound. Also pulled the cover off the front differential and the gears seem ok (no missing teeth, plenty of fluid, etc).

I did find that one of the bolts on the tranny mount had backed out - I tightened it up but there were no changes in its behavior.

While under the Jeep I noticed that his front driveshaft does not spin freely - should we start looking at the transfer case or tranny for the problem? I was focusing on the front axle based on what the shop said.

On a side note - I have a '91 Sport 4WD and after comparing the two, I noticed that my front driveshaft does spin freely while in park. Have I stumbled upon a clue or are they just different because of the years? Option wise - the two Jeeps seem almost identical.

Do you "feel" the skip in the accelleration, or is it just that you hear it and maybe feel the vib?
Your 91 probably has the vac disconnect on the front axle, the 92 should not so his drive shaft will not rotate in park. I would start by raising the front axle, then you should be able to rotate things to listen for sounds. Look at the u-joints at the wheels, lock in in 4-hi and try to rotate the front wheels to feel the gears and such... I would start there seeing how it is only when you turn left,,,,, but the second place to look would be the rear diff. It could have broken teeth on the spiders or something causing a similar issue.

Thanks for tips.

You can definately feel the skip - it shakes the whole Jeep when it happens.

We put the front up on jack stands and rotated the tires every-whichaway. Never heard or felt anything out of place. Did not try it in 4WD, but we will.

Tonight, we're going to set the whole thing up on jack stands and see if we get it to make the noise but moving all 4 tires. Will also check the rear differential for any damage.