RE: MPX FUNCOPTER!!!
Ours had a nasty tail vibe which was caused by something in the main rotor.
I balanced the main and it did not get better.
I took the head off and ran the motor and found main shaft wobble.
I check the main shaft on the lathe and checked for runout and it was fine.
So, I put it back and tightened everything and the wobble is gone.
Took it outside and flew it and the vibe is finally gone.