RE: Futaba Servos
I have seen that happen for a few reasons.
One was from using a long cheap (hobbico) servo extension. I replaced them with the heavy duty JR's and the problem went away.
Sometimes the connectors get corrosion or moisture on them, and this will cause it.
The other time it was just a worn out servo. (I would guess the centering pot was shot)
I would try unplugging the servo wires and cleaning them first. Then try some different extensions (if the servo is on one!) and see if it clears up. If neither of those work, I would switch the servo out.
Good luck.