I'm having a problem where one of my motors and props won't spin properly. It's the left rear arm of the bird. Upon executing a Car to start the Phantom, the other 3 props start properly while the problem one tries to spin but spins slowly and hesitantly in both directions. It never gets going. I did perform a basic IMU calibration last night. Nothing else. All software is at most recent versions. What's going on... Should I send it Back?