Motor clicking

A guy just left with his bike. It came in because the motor was making a loud clicking sound and he thought it also lost some power. I told him what it would be to take apart the motor and do diagnostics and maybe repair it at the sametime. It would make the sound whenever it rolled. I was skeptical because it did it forward and backward. What it was, was he used a one inch long zip tie to reattach the aluminum fender and never trimmed it. The knobs on the edge of the tire were rubbing it and the fender acted as an amplifier.
 
The zip tie was very small, in shadow and next to the black tire. What made me really look closely was the specific resonance of the fender when tapped with a tool, it made the same tone. That bike was offset by another bike yesterday. That was to be a half-hour job, but it took three. If you put it in the lowest power level you had to pedal three revolutions before the motor would kick-in then it would surge enough to buck the ridder and then stop and throw a code. If you started with the throttle the motor made a shuttering sound then lurch forward, stop and throw a code. It was possible on that bike to program it so you would only get power when pedaling backwards, making for a great practical joke.
 
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