I have a Radrunner1 with around 500 miles on it.  Recently it has begun making a chunk chunk chunk rotational noise when applying the rear brakes.  When spinning the rear wheel freely on the center stand and braking, I do not hear the noise, it only happens when there is a load/person on the bike.  I also do not see any abnormalities when spinning the rear wheel.  The wheel and brake rotors appear to be straight with little to no wobble, and the brake pads have plenty of life on them.

My worry is a problem inside the motor.

Any help is appreciated.

Thank You

Has anyone looked into or know of a Radrunner that has had gears installed?  There is plenty of room back there and the dimensions seem identical to the Radrunner Plus which has gears.  Same question for the suspension fork.