so i clipped a tree branch yesterday with my 5inch and one of the motors started making this low grinding/scraping sound when it spins up. not constant, kinda intermittent, like it only does it at certain throttle ranges. props are fine visually, checked them twice. no obvious bent shaft from what i can tell but honestly hard to tell sometimes.

ran the motors in betaflight motor tab and yeah motor 3 is definitely the one. the other three sound totally normal. im guessing a bearing maybe? or could the magnets have shifted inside? ive had crashes way harder than this and motors were fine so kind of annoyed this happened from a dumb tree tap.

motor is a T-Motor F40 v3 2400kv if that matters. worth trying to open it up or just swap it out at this point?

probably a bearing yeah. the F40s are actually pretty easy to pop open if you have the right hex bits. sometimes you get debris jammed in there too ? grass, bark, whatever ? and it causes that exact intermittent grinding you're describing. i'd pull the bell off first before writing it off completely, sometimes it's nothing and a clean + a tiny drop of bearing oil sorts it right out.

that said if you spin it by hand with no power and still feel any notchiness or roughness, the bearing is probably done. not worth trying to replace the bearing itself on a motor that cheap, just pull the whole thing. T-Motor usually runs like 15-20 bucks for that model so not the end of the world.

could also be a bent shaft even if it looks ok. like visually straight doesnt always mean its actually true. i had one that looked perfect and was causing vibration and noise and when i finally just swapped the motor the problem went away immediately. sometimes you just cant tell by looking.