Ian,

I had a similar problem with Futaba 9202 servos that I had in a CJM F-104. The problem only seemed to occur with a fully charged 4 cell battery pack. The servos seemed to jitter less as the voltage of the battery pack dropped. At 5.2 volts the jittering stopped and the servos were rock solid. I switched from a ppm receiver to a pcm receiver and it eliminated the problem completely.

Paul