I have a 2013 AWD that is making a loud noise and vibration at highway speeds. It sounds like it is coming from the rear center of the vehicle. I inspected the differential and it is pissing out fluid. The dealership (its under warranty) told me it was the PTU.. Noise stayed the same after they replaced it. Now I brought it back and they're telling me it's the tires. I have the Goodyear RSA's on my car with 7/32 tread all around. It is a constant noise that doesn't change pitch and it is loudest around 60-70mph. How are the rear differentials on this car? Do they commonly make noise?