so i binned my 5inch pretty hard into a concrete wall last weekend, classic story, was flying a gap i've done a hundred times and just misjudged the wind. anyway three motors are fine but motor 3 is making this sort of grinding/rubbing noise when i spin it by hand. not super loud but its definitely not smooth like the others.

thing is it still flies, props on and everything, hovers fine, does what i tell it. but that noise is bugging me and i dont know if its worth replacing it now or just keep flying until it actually dies. the magnets look ok from what i can see and i cant feel any wobble in the shaft. could be a bent shaft that just isnt obvious? or maybe debris in the bell?

running T-Motor F40 Pro IV's if that matters. been flying this build for about 8 months so not super precious about them but also dont wanna buy a new motor if i dont have to

bent shaft is my first guess honestly. even a tiny bend wont always be obvious when you look at it but you'll feel the vibration in the logs if you pull your blackbox data. check your gyro traces on that motor ? if you see a consistent oscillation pattern that wasnt there before the crash thats pretty much your answer. flying with a bent shaft isnt the end of the world short term but it WILL chew through your bearings faster and you'll end up replacing the whole motor anyway just at a worse time, usually mid-pack over something you dont want to lose

i'd pull the bell and check for debris first since thats free, but if its the shaft just swap it. F40s arent cheap but they're not crazy expensive either and your other components will thank you

had almost the exact same thing with a different motor brand, flew it for like two more weeks thinking it was fine and then it just let go mid-flight. not saying thats definitely gonna happen to you but yeah. the grinding is usually the bearings getting damaged from impact, even if the shaft looks straight