Is my stock rearend going out?!?

[Phantom]

K so I'm doing a brake job and after removing the rear wheels, calipers, and rotors, I grab the hub and try to spin it and as I'm turning it I hear some pretty loud noise coming from the differential. Also when turning the hub it doesn't just freely spin, it's hard to explain so forgive me for this lame explanation, but without the a poping "noise" it sort of pops while your turning it. This happens equally on both sides. About five thousand miles ago my buddy and I cleaned up the differential and put new fluid in it and it appear to be in good condition. Also when driving it I don't here any noises from it and it seems to be working fine. I guess in a nut shell I'm hoping this is normal and what I'm thinking is "bad" is in fact the TCS that is making this happen. Thanks for your help in advance.

[c5z28]

Is it an open diff or an eaten locker (should have the g80 code on the door panel if it is)

[Phantom]

Yes g80 is on the door panel.

[Cutlass]

If it feels and sounds fine while you're driving then I wouldn't worry about it.

[Too Fast]

+1. No noises while driving = should be ok.

Have you ever turned a RWD axle like this before? You can feel the gears inside the diff when you do this, could be all you feel.