At about 15 miles an hour it becomes noticeable. Then as I get faster and put more of a load on the gears, it gets louder. That sounds quite like me. Im at 55,000 Miles. 5,000 more and my warranty on that is up. So now is a good time for the gears to start killing themselves. I do have a little slack in the driveshaft. Or at least more than I had 25,000 miles ago.