It's likely to be a consequence of either the finite resolution of the stepper motor, or quantisation applied by either the slicer or the CAD program that generated the STL file when processing curves. It's unlikely that the stepper motors will respond to individual 1/64 microsteps.
If it is due to finite resolution of the stepper motors, then increasing the motor current may help, and changing to 0.9deg motors (which will probably require a reduction to 32x microstepping) will help.
If it's due to quantisation in the CAD program, there is probably a setting you can adjust if you have the original CAD model.