Originally Posted by antslake
That sounds like a broken arm, or a bad motor to me. The noise you hear could be from a vibrating crack in an arm, or a couple motors fighting each other and causing rpm differential noise. Flex your arms a little and look for cracks. Take the motor, and try to wiggle the outer casing separate from the inner and see if there is any play. Double check all your screws. That vibration you are hearing is driving the FC mad.
I had a bad motor from DJI, when I grabbed the outer part of the motor and wiggled it, it would make a clicking sound. Putting replacement bearings in did not help. I had to swap the motor, then my quad flew 100 times better.
I think you may have pinpointed the problem. The arms are brand new and I've never had a hard landing or crash, so I'm about 99% sure its not a cracked arm. However, when you mentioned a clicking sound from a motor when you wiggled it, that jogged something in my brain that I remembered that happening. So I went back and wiggled all my motors and found one that had a small click to it like the outer case moved a bit when wiggling. The other 5 motors had no play in them at all. So perhaps this tiny thing is whats causing it.
I talked to the store today where I bought it and they said they'd be happy to look at it and help me troubleshoot it if I can come in on Tuesday when their 'quad guy' is there.
Hopefully this will resolve it because I really want to get this thing flying!