The first thing to check is the wiring between your battery and receiver. A dirty switch, to small a gage wire, excessivily long leads or dirty contacts can cause the problems you are seeing. As a test, plug the battery directly into the receiver (bypass the switch and switch harness) and see if the problems persist. If they do, then check all the connections between the servos and the reciever by just connection one servo at a time to see if and when the problem reappears to weed out any bad connections between the receiver and servos. Of course make sure your battery is fully charged first.