I have an S9650 servo with a Telebee HH Gyro and it drifts, too. The gyro instruction manual says, "When the gyro is ready, the rudder servo may run to one direction (when the gyro is in head lock mode). This phenomenon is NORMAL."

I'm a little confused myself. What good is having an HH gyro if it normally drifts to one direction or the other? Sub-trim doesn't fix it, either. In fact, I haven't found any parameter in my DX6i that does. In another fact, I haven't even flown my heli, yet. I'm reluctant to until I can find a workable solution to this problem or just don't use a gyro at all.