to me it sounds like a bad motor. i ate the cost of a feigao doing the same thing. i thought i was smart so i popped the motor open to look for an issure and it turns out the rotor was unballanced which whipped the bearings and scored some of the windings inside. then when i reported this to the seller, they said if i opened the motor there is no warrenty. i was so mad since i only had the motor for 1 day, and only drove the car about 50 feet.