I posted this in the other thread -
http://www.camaro5.com/forums/showthread.php?t=233565 - that I didn't even know existed until recently so I'll post it here too because it might help others.
My dealer got sick of me coming in for the same problem all the time and finally changed the gears in the diff. Technically it was the clutches but they're inside a huge ball of gears etc that they said they had to send back whole for the warrantee so it was kind of replaced as a unit. Hopefully they put in the new seals and nut and fluid and additive and everything thing one more time else so it won't happen again next year! Seems great so far... no noise and it accelerates and corners SO much smoother without the rear axel binding up all the time. Such a perfect car otherwise and I totally love it still so it's a shame that there's this one problem for so many.