I am posting this to save others time in case they make the same stupid mistake I made. I've got summer and winter tires mounted on two sets of wheels and I swap them out each season. Been doing this on all my cars forever. Swapped the winters off my Model X and put the summers back on, and then noticed a grinding sound on both fronts, especially when turning and reversing. Normally wheel grinding is a bent heat shield or rock in the rotors, but after checking them and pushing the heat shields out, the grinding was still there. After days of searching, I finally discovered what most of you probably already know: YOU DON'T ROTATE MODEL X TIRES. I had moved and crossed over the rears to the front, and of course the sizes are different from front to back, so, duh, they didn't fit right. Anyway, hope this helps somebody out there save some time.