I have noticed the past few weeks when I drive without traction control and let the rear loose around a turn I hear a "clunk" from the back. Does it when turning left or right. I tried going back and forth and it does it once per turn. Fairly loud, almost as if something was in the trunk flying back and forth (I did check and nothing is there, also took all of the flat tire crap out except the foam).

Any ideas where I should start looking?