I have 4 of the 5 amp 570 in/oz nema 23 steppers. I finally got my machine up and running but I am having an issue with one of the motors.
If I only have my Z, Y and A motors plugged in all is well but when I plug in my X motor ALL the motors start to make a kind of hissing,buzzing noise at idle.
Unplug the X motor and all go quiet. Plug it back in and all get noisy.

Here is a grid of what I have tried
Motors plugged in
A X Y Z noisy
X Y Z noisy
A Y Z quiet
AX noisy
AXY noisy
XY noisy
XYZ noisy
YZ quiet

So you can see the only time the motors get noisy is when the X motor is plugged in.

I am using KL 5056 E drivers
I am running Arduino/GRBL
The X and A drivers are connected to the same port on the arduino.

I think I have a bad motor.
Please help.