I noticed something a little weird today while out flying. When coming out of a 180 stall turn, as I level out and accelerate across the field I noticed the heli develops a quick porpoising motion. The nose quivers up and down quite rapidly as the speed increases. Not bad enough to lose control so far but it's the only time the heli isn't rock solid while flying.is this normal or is it something I should keep an eye on?