I purchased my 09 CTS-V on Jan 2, 2009. In June 09 I noticed a popping/clicking sound coming from the front/passenger side. Dealer removed wheel, cleaned rotor, wheel, etc. and sound disappeared. In Sep 09, a similar but louder sound started in the driver/front side - especially during turns at slower speeds. Dealer replaced front left rotor assembly - seemed to fix the problem. In Dec 09, both driver and passenger/front popping sound started during reverse out of parking space (left and right reversals). Dealer was able to replicate consistently but determined this to be 'normal condition for a limited slip differential as compared with another, like CTS-V" on the lot. Today (Jan 7, 2010), the front end pops loudly and the front end of the car 'hops' when reversing out of a parking space -- every time. I contacted my dealer on Jan 6 stating the condition is unacceptable and requires further communication with GM engineering.

Wow that doesn't sound good at all. Best of luck getting GM to actually fix your issues.

My 2012 had a roaring noise from day one. I took it to the dealer with a few K miles and they replaced the entire differential. They said GM wanted the entire unit sent back to them. So they didn't even open it up.

After the new unit was put in, it eventually started roaring again or at least I thought it did. It wasn't sure until my 2013 arrived that I realized the rearend on the 2012 had actually gotten very loud. By that time the 12 was at auction and had sold.

I did not have a failure of the diff, but klunking & whine from the diff. Dlr said it needed to be replaced at 52 k miles. New diff has 3k miles and displays the same symptoms.
Dlr says the new diff has a new part # so it must be new & improved. Only driving that might have stressed is hard acceleration. This driving me nuts, because otherwise I love the car.
2005 CTS V sedan