Ok I am new to the group but not new to Mustangs. This is my 7th. But here is my issue. After owning the car for a week the stock gear was driving me nuts. Car is an 03 GT 5 speed convertible 97k on the odometer . I took it to a local speed shop that is basically across the street from my car audio shop. Seemed to be nice guys and they had done my xpipe a few days earlier so I took it back. Bought ford racing 4.10 gears with install bearing kit from American muscle . And a crush sleeve delete kit off ebay. They installed it and as soon as I picked it up and drive it I heard a noise . The noise sounded like an all terrain tire when slowing down. Hope that makes sense . It was way more noticeable on the coast side of it . Clutch in or out doesn't change the noise. So I took it right back and they put it on the lift. Pinion gear is loose and leaking. They stay late and take it apart and reinstall it . I drive it and noise is still there so I take it back the next day and tell then we need to try this again. They order a brand new gear set and install kit and I bring in a very good friend that has a daughter that raced circle track and he has done a ton of these 8.8 ring and Pinion to help set up the ring and pinion. He set the backlash on 12. Whatever that means . Don't know as I am not a mechanic. He also said the pattern was the best he had ever seen. He put it all back together and we took if for a short drive and parked it for 24 hours. I drive it for a short drive and let it set for 24 more hours. Drive it around town and the noise is still there . And it's most noticeable on the coast side not acceleration side. But I have no cats and Flowmaster with dumps. So it's kind of hard to hear anything but the exhaust on acceleration. Now the guy at the speed shop says he doesn't know what it could it be as they all 3 checked everything on the last install and everything checked out. My buddy is super anal about stuff and he said he agreed with the speed shop he doesn't know what could be causing it. Here are my questions. Could the first bad install habe harmed anything like the axles or something? Has anyone ever heard of this same noise after a Ring and Pinion install. Is there anything we can check . I am taking the car back on Monday so they can put on the lift and check things. The ring and Pinion isn't leaking at all. My buddy said when the first guy installed the first ring and Pinion that he had the spacers on the drivers side and he always puts the on the passenger side . Not sure what that signifies sorry I wish I knew more about rear-ends. I can install any car audio in this world but a mechanic I am not. And please if anyone has suggestions please share . Sorry for the novel