Yupe mine too, but only after a slight lift did the slight grinding start, and it sounds exactly like you are describing. My dad thinks it has something to do with the larger heavier tires/wheels and different tread pattern.
Jay and I have talked about this before, and I totally agree with him and this grinding may sound like it is coming from the rear, but actually is occuring because of the lift/change in axle angle, even a slight change.