what axis was it twitching on? if its the yaw axis, you may have issues with your gyro. my rex twitches from time to time in yaw because i have my sensitivity to close to the dead band of the gyro. i may be mistaken, but if you move the tail pushrod to a hole closer to the center of the servo horn, you can increase sensitivity and therefor be rid of the tail twitching. good luck, and let me know if this helps.