I heard somewhere that with expensive coreless servos, they give a little jitter when turned on to check their center. I think that it was the FAQ page at
www.futabarc.com
You should always turn on your TX first, then your receiver, and turn off the RX first, then TX, as if for any reason the engine should start up, your throttle will move and maybe go to full. I saw this happen to an electric once, when he turned on the RX before the TX, the throttle opened and it went full bore. It stopped in long grass, but if someone happened to be infront of the plane, it could have been bad.
Hope this helps.
Robert.