two things to check. First the easy one: Check that the motor connector by the back wheel is all the way in to the marked line, not just in tight. next, you need to have a look in the controller compartment at the front of the battery where the motor connections are. Somebody else found melted wires in there, and you can get other connection issues. Make sure everything is tight.Update.
Unable to find loose wire.
If I twist the throttle I can hear clicking from the controller.