getting rear differential replaced due to a clunking sound when driving. anybody else having similiar problems?

I think that you're the second one that had this. The other was a guy that had a part go in the locker on his so he had to get the entire thing replaced by the dealer since they said it'd be easier then trying to get the entire thing apart to replace something like a couple dollar part. Keep us updated about the cause if you can find out.

Does anyone know if it is the same rear diff. used in the Titan? I would ASSume it isn't, but with all the platform-sharing Nissan does I guess you never know. The reason I ask is because it seems a lot of Titan guys are having rear axle problems due to a faulty pin of some type...

All Titans got the M226 (D44-based) rear diff, but most Xterras get a revision of the old C200 diff that's been around for decades. The locking diff in the Nismo trim definitely gets the M226/D44, but otherwise only the 6-speed models get the open D44.

We just got an 06 S auto.

When starting moving we hear a clunk from the back of the vehicle. I dont hear it when moving.

Does this sound like the same thing ? Funny if it is because I had an 01 a few years ago and had to get the rear diff replaced on that one.

That clunk you hear is the ABS. It goes through a self test when you first start the car.

Thanks.