I have the exact sound on my 2010 M6. I took it to the dealer this week. I took the tech for a drive and he heard the sound and said that he never heard that noise before. They call me later that day and state that the noise is normal...
So I insisted on driving another SS M6 to see if it makes the noise. They gave me the keys to a brand new 2011 SS M6 with 2 miles on the clock. Guess what, it makes the exact same noise....
I can't believe that this noise is acceptable to GM. The first day I brought my car home from purchasing it my neighbor was outside when I was pulling it up the driveway. The first thing he said was "what the hell was that rattling noise". How freaking
embarrassing 