I am trying to diagnose a whirring or whining noise coming from the rear end of my ’03 GT. I did a lot of searching in here and on the web, but I had a couple of questions that I could not find the answer to. First a little background on the car: The car has 85k miles on it and is driven on a regular basis, although not daily. I had the carrier and pinion bearings replaced by a pro mechanic about 12k miles ago, so I do not suspect those are the issue, at least I hope not. The diff is the original that came with the car. I also do not have any leaks coming from the differential, or from anywhere else. I usually hear the noise at about 45 mph upwards, and it is most noticeable on the highway. It’s pretty constant and does not really change pitch with when I give some gas or on deceleration. No change in the noise that I have noticed when turning. I have not done the rear brakes or wheel bearings. I jacked up the car last night and noticed some in and out play in both of the rear wheels. The passenger side had more play than the driver’s side. Is that type of play normal? I tried to wobble the wheels too, by pushing on top and pulling on the bottom of the wheel, but they felt pretty solid that way. When I rotate the wheels, they move freely but make a light rubbing sound. I also notice a little play where the wheel would move a bit before the drive shaft engaged and moved. Does anyone know if that is normal? I have noticed that on the highway, especially in 5th gear, there is bit of thunk when going from coasting to getting back on the gas, and you can feel it re-engage. I appreciate any help with this or any ideas/suggestions before I start throwing money at it.