Subject: Tire size - Transfer case problem My 07 X3 has recently started making some ugly noise when slowing down with out using the brakes. It makes a noise like rolling over a cobble-stone street as it is down shifting to 2nd 1st gear. Shift into neutral and noise would go away. Step lightly on gas and noise would go away. Key point take away the back pressure on transfercase and transmission and noise goes away.
I took it to the local dealer and they told me it was "bad tires" after a few exchanged words they mounted some brand new tires and took the car out for a test ride and the noise was gone!
A few miles ago my wife tested the sidewalls of the rt-front tire against the curb, tire lost, so we replaced both front tires with exact matching Pirelli Scorpion tires. This was at about 33K miles on the car. The car now has 37K miles. So front and back tires have about 33k difference in mileage. And making noises.
So BMW Munich says if you replace 2-tires, must replace all 4-tires. If the tread wear is "significantly different". No additional info on what they consider a "significant difference" in tread wear.