'96 3.9 4WD problems
 

I just bought a 1996 Sport 3.9l with the 5 speed manual. So the problem is with the 4 wheel drive. It shifts smooth into high, low, and neutral, but makes a horrifying bumping/snapping noise when moving. I guess it's probably a stretched chain and I'm gonna need to dig into the case, but I'm hoping you knowledgable folks know any common problems with these trucks that would cause this. Bad CVs?

Timing chain

Negative. It's only when it's in 4WD, only when it's moving and under load, and sounds nothing like a loose timing chain, and In fact is not coming from the engine at all. It's obviously drivetrain related, and i'm about 90% sure the chain (In the transfer case, not the engine) is stretched and skipping teeth.

Ah. Well at least you know what the timing chain sounds like...

Well, if it only makes the noise in 4WD, its probably not the CV joints as they are always turning when the truck is moving. The stretched transfer case chain is a common issue, and is often caused by driving on dry pavement in 4WD. It'll make noise, and it'll chew through the cast aluminum case if left to bang around for very long. The good news is that the T-case is relatively easy to rebuild if you're mechanically inclined, and rebuild kits with chain are available for less than $200.