[DoctorDex]

I found this info that I thought might be helpful. From this post, by Bret Brinkman, it sounds like it isn't a bad VCU/output shaft problem causing the backlash:

"First off, the floppy carrier bearings every one points the finger at came floppy from the factory. Sorry to inform every one, but you all wasted your money. I have never heard of a bad carrier bearing. All though I will say a CFDS is an excellent mod as it eliminates the noises and vibrations the carrier bearings made even when new. It is easy to see if one of your U-joints is bad because it will have back lash in between the two shafts it connects. Some times they will develop a squeaking sound when they fail also.

If the sound is coming from the rear it could be excessive backlash in the rear diff. You should consult your repair manual for details on checking and adjusting the back lash. Any one that doesn’t have a manual should stop screwing around and get one. They are an invaluable and nessisary diagnostic add as well."

Here's the part I found really interesting:

"If the sound is from the front then it is probably excessive back lash from the center diff in the tranny. The back lash is caused by very hard and very sudden launches such as high RPM clutch dumps. During such an event the dowel pins in the planetary assembly (part of the center diff) SLAMS against its aligning holes in the VCU (also part of the center diff). This hammers the holes out to make them a larger diameter which results in increased back lash (there is some from the factory keep in mind). Once it starts it becomes easier and easier to make it worse. What I would like to see some one try (I’ll probably end up trying it myself) is to tap out the dowel pins in the planetary assembly (they tap out with a hammer), find a drill bit the same size as the holes for the pins in the planetary assembly, line up the planetary assembly with the VCU, and drill holes into the VCU that are the same size as the holes in the planetary assembly. That way you could tap the pins through the planetary assembly and into th VCU. It would be a press fit and thus zero back lash to begin with. Which none to begin with it would eliminate the hammering effect altogether. The other fix would be to replace both components. I did not add this as a weakness of the drivetrains because it doesn't actually fail. It is just annoying."

The post I'm referring to can be found here: Everything you need to know about your AWD drivetrain.