Robin2:
Measure the resistance of the motor coils. Measuring voltages is unlikely to be useful - especially if you are not using an oscilloscope.
Well, I'm talking about the voltage while the motors are idle, so they weren't really fluctuating much. There's quite a difference. It seems suspicious.
What I was able to do is hook up the "Enable" pins on the TB6600 to pin 8 on the Arduino, which makes the motors only get power when I send a G-Code command to GRBL. While moving, the motors are very quiet! Almost zero whine because GRBL cuts the power as soon as movement completes. This is a somewhat acceptable work-around for now... But I'd still like to work this out.
MarkT:
Adafruit motor shield? I thought we were talking about a TB6600 stepper driver? You can't drive
a low-impedance bipolar stepper with anything but a stepper driver, DC motor shields are completely
unsuitable and will burn out.
It's made for steppers and DC motors, which is why I was able to drive my steppers with it, like I said. Here's the link to it again: Adafruit Motor/Stepper/Servo Shield for Arduino v2 Kit [v2.3] : ID 1438 : $19.95 : Adafruit Industries, Unique & fun DIY electronics and kits
MarkT:
Its pretty normal for a stepper to make noise, BTW, even when stationary, due to the chopper
oscillator.
People say this.... but they made zero noise at idle when powered by the Adafruit motor shield, even though (it appeared) voltage was going to the coils, like I said in my previous post. Neither of the drivers made much noise while the steppers moved. Also, I'm not talking about like a quiet whine like a television... it's really loud. It genuinely makes me nauseous to be in the same room with it for too long.