Began to hear a bad roaring sound coming from the rear of car. Took it to dealership to get checked out. Apparently the rear differential is known with the CTS for going out at around 80k miles. Thats already a red flag. Also, there are no replacement differentials available. Oh, and also it can't be overhauled because it's a system of clutches, compared to normal differentials. Basically, at 80k miles the car is totalled.