That's cool but that is something I get all the time with the Keling 6050 drivers and it happens on every motor on every cable. It really depends on where the motors are when they stop. It's the chopper circuit in the drivers that causes the noise and dad was right, it's in the upper audible range as I understand it. Generally it quits as soon as I step in any direction by any amount. Not enough of a deal to get in a twist over to me but yeah it can get rather distracting when it's loud. I don't always get it but usually I do.
I didn't think much of it because when I was playing around building my own drives they always did the same thing when they powered up after a disable, or power-off so I was used to hearing it.
CNC: Making incorrect parts and breaking stuff, faster and with greater precision.