I have had similar problems with other JR servos when I used 5 cell packs. I use a lot of the 8611A. If you drop the voltage to under 6.0 I bet the problem will go away, at least that is what Horizon has advised me to do. they will only recommend up to 6 volts now. I use Lion on areulator set at 5.7 volts, large turbine aircraft, and the 8611A has plenty of power at that voltage.