I have a quadcopter controlled through KK2.1.5 flight controller. I have been flying with it without problems, but now i am facing a problem. When i start and arm the kk2.1.5, by giving throttle it starts turning towards some direction with acceleration. I double checked the motor pins locations and all other things, they are correct. When i took a look to the gyro bubble of kk2.1.5 it wasnt at mid of the crosshair. I turned the quad off and then on. I check bubble again it was at centre. now again when i gave it throttle it started turning towards some direction. I checked the again, and it wasnt on centre this time too. So at the armed state the gyro bubble moves away from centre by giving throttle. due to which quad overcorrects itself. Now i have understood that the gyro is off centre due to vibration of the FC. What should i do to antivibrate it. What material should i keep in between so that vibrations are almost zero.