My wife somehow got a rock caught between her rotor and rotor guard on her car one time and it sounded wayyyyyyyy worse than what it was. The screeching was horrible. I once replaced spacers on my car with ones a few millimeters narrower, did it all went to move the car and it woukd only go about 4" and stop. Wondering what was going on I figured out the lug bolts (not nuts on a bmw) were now too long and getting hung on the rotor guard. Had to cut all of them down with a Dremel. That was a headscratcher but figured it our, I was like what da ****!