RE: Servo on the way out?
What RX are you using? Some of the Futaba HS Rx do not support digital high speed mode on all servo channels. For example the 6008HS supports the high speed mode only on the first four channels. The buzzing occurs only on the high speed channels if high speed mode is selected. Typically ailerons will be connected on 1 & 7. In this case, if high speed mode is enabled, channel 1 will buzz but channel 7 will not. Racked my brains as well till if figured out this. If thats the case, look at going to normal mode (see the manual for how to set this) and all servos will be ok.
If the servo allows the control surface to drop when the TX is switched off, it just means some play in the gears. It varies from servo to servo. The 3010s on my airplanes do not allow the surface to move when the RX is off but the 5625s do.
Ameyam