Last few times out with Nics Nazgul it got a noisy motor intermittent. Changed props flew today flipped on take off , then re flew and was flying then flipped out. took home ran on betaflight all seems ok. Not sure if a small stone fell out or was that from crash flipping, Any tips for checking would be good.
Sounds like a desync, which is generally a bad motor.
One may have a bent axle.
Spin them slowly by hand and visually check that the gap between bell and magnets is constant all the way around.
Fasten up to betaflight configurator with battery and run each motor up manually on the motor tab. Without props of course. Whilst doing this look at the gyro trace on the same page and see if one of the motors is vibrating more than any of the others.
If you find a bad motor, replace it with a new one.
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I spun by hand slowly thats when 1 locked slightly and the small stone dropped. I did run in betaflight and no vibrating. when we flew nr you at chesterfield we seemed to get a lot of magnetic debris stuck on side of motors ,was thinking that slight piece may be inside locking motor. Need to do a test flight again cheers for the advise
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Yeah that place is terrible for magnetic dust. Never ever try to turtle and don’t crash (if possible)…
Take your motor apart and clean them out, its really easy 
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