title_body: Grinding sound on FPV motor but no apparent damage
upvoted_answer: It looks like a bad phase to me. Check the resistance of each phase, wire 1 to wire 2, wire 2 to wire 3, and wire 1 to wire 3. If one of those is much higher resistance or shows no continuity, then you've got a bad phase. I suspect this is the issue.
  
  Also try swapping the motor to a different arm. This will eliminate the ESC as the issue. If the problem follows the motor to the new arm, then the the issue is the motor, if it stays put then it's the ESC. A bad FET or gate driver in one phase on the ESC can cause the same symptoms as a damaged phase in the motor.