2005 Vibe noise help

[boog22]

I have an 05 Vibe awd, just recently my wife has told me it is making a loud clanking nosie(similar to metal hitting concrete). I have took the car out and I can hear the noise but it is not very loud but she says it can get loud at times. The noise seems to be coming from the rear of the car. I crawled under to check to see if anything is hanging and found nothing. I did notice that the rear differential is leaking very little(not enough o even leave oil marks in driveway) and was not sure if this would relate to the noise. I am thinking it is muffler or cat converter that may be going and have the rattle inside but not really sure. Anyone have similar problems?

[Serj22]

4wd rear differentials will make clanking, or humming noises when the diff has become "dry". Meaning the fluid has been leaking over time. It may only be leaking a little now because a majority of it is already all over a freeway somewhere. Take the car out to an empty parking lot and have someone sit in the trunk with the rear door closed. Make hard u-turns in both directions. The noise should get louder as you circle, but quiet down when you are driving straight. If this happens, the differential is likely dry, and the fluid will need to be added and the gears will need to be " burnished" after, then new fluid inserted.

[boog22]

Thanks for your advise, any clue how much something like this will cost to repair? Would something like this be included into a powertrain warranty?