Now to figure out why during a spin up/spin down (pre-lift off) the tail starts to chatter.
If you're using a HH gyro, its possible that the tail rotor control is up against a stop. Does the heli tail jerk to one side or the other just after liftoff? If this is the case, then you may need to operate in rate mode until you're just about to leave the ground.
OTOH, you could have an unbalanced tail rotor.