If the problem is not caused by the main blades then i am sure that the motor is not working properly and is nearing the end of its life. The vibrating is caused by the main motor not functioning consistently which means that it does not hold a steady RPM but it rather works in "bursts" of power. You will have to replace it with a new one . If your heli is gear drive (tail) then install a GWS 280 heli main motor (also known as EDP150/H) available from Tower Hobbies. You must also install heatsinks in both the main and tail motors otherwise they will overheat , not run smoothly and eventually fry. Heat is the worst enemy of an electric motor (especially micro and tiny ones). Also , adjust the mixer gain value to a 2 o'clock position and the gyro gain to a 3 o'clock position.

Good luck.[sm=thumbup.gif]