Could be in your tranny. I had mine rebuilt because I grenanded it, (someone has anger issues...lol) and they left a bushing out. It whined in every forward gear but 4th. Someone on here (Or possibly another Jeep forum Q'tec) told me it was probably a missed bushing and that the gears probably weren't meshing correctly. Took it back, told them what I had found online. They looked it over, said it was their mistake, rebuilt again, whine gone. Just a thought.