weird squealing noise on my steppers when not testing my motors - 7i76e, DM556

Hello! So I'm working on building my first CNC and i'm running into some problems with my final assembly. If i'm not testing my steppers in pncConfig, or running the actual linuxCNC program, my stepper have a loud, high pitched squealing sound coming from them. This is what it sounds like:


I'm using a Mesa 7i76e board, DM556 drivers, a 1300W cisco power supply to get 42V for my drivers, and nema 23 steppers. my machine is an XYYZ machine if that matters for any reason. Here are the steps and states of things as I go through them.

1. power on my mesa and my 42V power supply
Status: able to ping mesa board, green LED on drivers blink continuously, motors quite
2. start pncConfig, configure it with my stepper setup and mesa type and address, and get to X Motor Test/ tune page (but haven't clicked test button yet)
Status: green LEDs still blinking, motors still quite
3. click the test/ tune axis button
Status: green LEDs turn solid on all the drivers, motors quite
4. enable the motors, jog + and -, and click run
status: X motor moves as expected. when not moving it's quite. All other motors stay still and quite
5. exit the test (either through cancel or OK button
status: all the motors start making squealing
6. go forward to Y motor test page, and click test/tune axis
status: all motors go quite, and Y motor moves like normal and acts as expected.

I complete the pncconfig so it makes the HAL and INI files. Without running the linuxCNC program, the steppers make the squealing noise. As soon as I open linuxCNC, the motors goes quite. While the program is open, the motors work like normal, but if i exit the program, my steppers start screaming at me. if just restart linuxCNC program, the stepper squeal for a second or so, and then go quite.

I tested my steppers and drivers a few weeks ago when i got them, and everything seemed to work fine. no weird noises or anything like that.

All my steppers, and sensor cables are shielded (foil), both inside my electronics enclosure and outside. I have panel mount connectors to get the cables inside my enclosure. I'm powering my mesa with a 24V 5A supply and my steppers drivers with a 42V supply.

I've tested with grounds from both my 24V and 42V supplies connected to my earth ground bar, and with just the 42V ground connected to earth, and with neither connected to earth. I've also disconnecting all the motors and hooking them up one at a time to each driver... same problem (squealing noise when not testing, working as expected when testing). I've also ohmed out the terminal block on the drives that connect to the steppers and the mesa board (with them pulled out of the driver) to make sure nothing was shorted together or shorted to ground.

for my mesa to driver I'm wiring connecting things up like this: imgur.com/a/paWVp9Q .
I'm only using the step+, step -, dir+, and dir- pins from the mesa. I'm not using an enable line to my drivers (should i be?).

I've attached my HAL and INI files. I know i can run my machine by powering on and off my drivers only when i'm using them, but something seems like it's not quite right and i'd hate to kill something on my setup a couple weeks from now because I have something wrong. I'm not quite sure where else to go from here, so any and all advice is more than welcome. Thanks a bunch!

Edit: one thing i didn't mention is that if I unplug the terminal block on the drivers for the mesa control signals (step/dir) before powering up the drivers, the LEDs turn solid green right after powering up

I'll try hooking up the enable pins tonight and test that out. Is there a way to have the enable pins toggled, so that i can disable the motors from the mesa board? I know each set of motor pins on the mesa has a 5V and Ground terminal (which i'm not currently using these), but as far as i can tell those are fixed and don't change. Can i perhaps use pins for either the 4th or 5th axis and somehow set those up to toggle between 5V and ground? If anything else i'll try just connecting the 5V and ground to the enable pins on the driver and see if that fixes it for now.

Also, the enclosure right now is an old PC case, so it's steel I'm pretty sure. it's not aluminum at least.

Thanks for getting back to me. I'll let you know the results from tonight.

Yes, if you don't use all the stepgens, you can use the STEP
and DIR outputs as 5V signals. They will be accessible as
GPIO pins in hal.

You might try wiring the STEP/DIR pins as single ended.
sometime the lower output drive of differential mode causes
issues with step drives. Changing to this mode would mean
moving the STEP+ and DIR+ wires at the 7I76E to +5V
instead of the STEP+ and DIR+ 7I76E connections.