We just had our 2011 performance in the dealer where we bought it due to a "kick" when hitting a bump at highway speeds. Figured it was a rear shock related issue but not sure. They couldn't feel it driving it but did do an alignment. The alignment did help somewhat but afterwards we noticed a thumping from rear end. Almost like the trunk lid bouncing however upon return to dealer it turned out to be a broken shock. We have the CPO warranty and are just outside of time on the Factory warranty but 12k under on mileage. They talked to the GM rep and they replaced both shocks for less than the deductible on the CPO warranty. We are very pleased with the response from GM!