Gungadin

Anyone besides me have issues with the Futaba S9550 servo developing a twitching problem after extended use ? The two that I have been using on my elevator started to chatter and twitch when I turn the radio on. Then when I move the elevator stick they stop. This didn't happen till I had about 50 flights on them. I see that Futaba has discontinued this model and replaced it with a S9551. Could this indicate their is a issue and the new servo has been issued to fix the problem. Could be a pot problem. Any body know ?