hey everyone. this is my first post on this website. I have an issue that I would like some advice on. I own a CTS 3.6L, 2005 6 speed manual transmission. I think my issue is with the rear differential. My problem is as follows: From a complete stop, then accelerating hard off the line I get this very scary feeling in the floor, and deep sound (repeat knocking) from the rear. This knocking gets faster as i go faster. It is stickly limited to first gear and only off the line. I have been told by a mechanic that this issue exsists in the in all cts-v's prior to 2008, being thats its also manual transmission. He tried to sell me a bracket thats after market to rectify/remedy this problem. Does anyone out there have a similar experience. He also said its something to do with warn bushings??? I can barely peel out anymore. (Not that I abuse my car, but its nice to be able to peel out). I was also told that continuing to drive without this bracket, would not damage my differential. To my unexpierenced ear, it almost sound like gears skipping the teeth. But then again what do I know. Please Help.