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Q: Knocking/fluttering in rear end

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I have a 2010 GMC Acadia. Last Friday my car didn't feel right. Thought I had a flat because of the fluttering sound in my rear end. Later that morning I Ended up getting a flat and a screw in the other tire (both passenger side.) they plugged the front and replaced the rear pass. No more noise. Fast forward to this Friday night noise is back as is a clunking sound. Took it to get looked at. Suspension is all good. They suggested could be the drivers rear tire is so different in tread depth that it is tricking the speed sensor to fool the rear differential. They suggested I change the rear tire and that should fix it. Asked if I was doing any further damage driving it. They said no. I drove it home yesterday and out today around town. Fluttering is worse and noisier. I'm sure it has something to do with the rear diff from everything I have read. So my question is... Any suggestion of next step? Will tire make that much of a difference? I have owned the car since 88000 and have no record

My car has 112000 miles.
My car has an automatic transmission.

Hi and thanks for contacting YourMechanic. If you have a limited slip differential, then having 2 different size tires on the axle will cause the limited slip differential to make this noise. Eventually, the limited slip will stop working and your vehicle will then drive normal with burnt clutch material in the differential oil. I suggest putting the odd size tire on the front of the vehicle and putting a regular size tire on the rear. If you would like to have another local expert inspect the car in person, a qualified professional from YourMechanic can come to your car’s location to pinpoint the proper fix.

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