does it sound like gear whine to you?
it may be a good idea to open up your differential and check for metal shards. at the very last, if you don't find anything wrong in there, at least it's a good opportunity to change your gear oil - always a good thing.
how are your tires wearing? check to see if your tires are wearing evenly. if you find, say, your rear right tire is worn a lot worse than the other three, then you likely have a problem not related to the gears or differential. if all 4 tires are worn evenly, that tells us something else. even/uneven tire wear tells us a lot about your situation.