After a hard crash yesterday, motor 3 on my 5-inch FPV quad is making a grinding noise and gets stuck at around 3000 RPM. Signs of motor problems include abnormal noises coming from the motors, uneven performance during flight, or the drone not responding to control inputs properly. I've cleaned it thoroughly and checked for debris - the bearings seem fine when I spin by hand. If the motor's speed is not normal, it could be due to motor damage, ESC failure, or power supply problems. Should I replace the motor first or could this be an ESC issue?

Simply trade your #3 ESC signal wire with any other signal wire, lets say #2. If the problem transfers to the #2 motor, you know it's the ESC. This will isolate whether it's the motor or ESC without having to desolder anything.

The copper windings of brushless motors are enamel coated, so the motors themselves are technically waterproof. With the motor bell off, you can spray some compressed air on the windings followed by a rinse under some warm water to clean out any dust and dirt. Try this first before replacing anything.

Had the exact same issue with motor 4 last month. If the issue persists after the previous step, the motor may have an internal issue and the affected motor(s) will need to be replaced. Locate the problem motor(s) and desolder the three wires attached to the electronic speed controller (ESC) after removing the heat-shrink tubing. Turned out to be a damaged bearing - $12 motor replacement fixed it completely.