the "cards in the bicycle spokes" noise is often from the motor armature commutator bars getting raised and larger spaces than designed for between the bars, the noise is from the bouncing of the brushes. this happens if the unit is 'stalled" (not able to turn) more than about 5 seconds with full battery voltage going to the drive motor.
This is ONLY to be used to report flooding, spam, advertising and problematic (harassing, abusive or crude) posts.