I recently purchased a 2003 Ford Explorer with 45,000 miles it is a 4x4 v8. I had the dealership look at the vehicle for a whining noise only heard in 1-3 gears and goes away in OD. The vehicle also occasionally has a knock followed by a jerk while driving down the road as if I ran over something in the road. The dealership tells me that I need the rear differential cover replaced, rear pinion replaced, Tension belt replaced, the Idler pulley replaced and that the ball bearings are severely worn. I had a Carfax pulled for this vehicle and found that it was involved in a rear end collision. My question is: Would the rear end collision create heavy wear on the ball bearings and will this issue keep popping up every 10-20 thousand miles?