random motion during animation

I have an assembly of a vehicle ascending a tower.The vehicle ascends 10 feet then I wnt it to start rotating about the tower. I use a rotary motor to start the rotation at a given time and key frames to accomplish the upward motion. The vehicle jumps up and down the tower randomly until the rotaion starts and then ascends fine.

What would cause the random motion until the rotary motion starts.

I have posted the file for your reference.

ANY suggestions would be greatly appretiated.