Welcome to the forum!
I moved your post to a new topic and fixed the formatting. If you put 4 spaces or an indent on the sentence (like letter writing style) the forum will format the text like a code snippet.
The whine is from the motors holding position when they become energized / engaged as current passes through. This is known behavior. Changing the current can reduce the sound, but make sure it is high enough to prevent skipping steps: Changing Stepper Motor Current
If you don’t want to enable StealthChop mode, you could send an M18 command in the LightBurn console to disengage the motors while not in use. M17 will reenable them again and you will have to home the machine so the software knows where the head is at in the work area. You could create macros to execute these commands in LightBurn, if desired.
How are you turning off the board? Can you provide a clear video of the exact steps you are taking and results you are getting and post it on YouTube or another site, then paste the link into a reply here?
I have mine plugged into a power strip to turn all of my laser components on / off simultaneously and it works beautifully.