I'd like to add one more thing to Rodney's suggestions: mechanical resistance. If pushrods or hinges are binding, the voltage could drop and make the LEDs flicker. Particularly if you are using a high-impedance NiMH or have any of the other problems that Rodney listed. The combination of mech. and electrical problems can easily cut the voltage in half under load. What I would do to check for mechanical problems is to disconnect all servo horns and wiggle the transmitter sticks. If the LEDs are steady, the problem is most likely to be a binding pushrod or hinge. If the LEDs still flicker with the servo horns disconnected (which puts a very small load on the elec. system), you have an electrical problem. Or there could be a combination of both.