It is most likely the Cage Bearing/Seal on the AWD system. At least that's what they suspect but would like to hear it, if they can. It won't happen unless warmed up and on a longer drive. This was a problem in 07-08 but was design changed in 09. It also requires a full drive shaft change with new cage bearings and seals. And the drive shaft has 4 sets of universal joints because of the length and geometry. Welcome to the world of AWD, more stuff under the car, more stuff to go wrong.