I have a 2018 Atomic zipper that has an irritating rattle. Any ideas. I thought it was the tin plates by the brake disk. Nope. I rattles when at high speed and let off the drive foreword peddle.
On a GEM, a worn out resilient bumper on the motor output shaft will give you a barking noise when you let off the throttle, especially from high speed.
Not sure about how the Atomic Squirrel Nut Zippper cars are put together, but maybe check the transmission & motor. especially if it has some miles on it.