strange thing happen when doing motor tuning

I'm build a stepper driver using L297 + L6203, and test it with Mach3.
I perform motor tuning, strange thing happen.

when I press "up" button the motor step forward smoothly, but when i release the button, sometimes it stop but sometimes the motor step backward by it self (and sometimes it step backward faster & smoother then I'm doing step forward)

also when the motor stop or just when I disabled reset button to enable the driver there are a noisy sound, is that an electrical issue on my motor driver?

any suggestion?