I have the same thing that I have had ever since I lifted. I can never tell if it is from the front or the back, but it only happens when I am off the gas normally around 2k RPMs. There are lots of threads but no one has seemed to really have a clear cut answer. I will search for that one thread a while back that was helpful, but I am still wondering what mine is, but it hasn't gotten any worse and I don't feel like fixing 3 things to find out it was something completely different and not really worth worrying about. Someone once told me it might simply be the new angle of the front drive shaft on the TOD system, I don't know really.

oh I found it:
http://www.vehicross.info/forums/sho...t=13537&page=2