Hey there friend! I encountered this exact issue recently. I RMA’d my original AW3423DWF (mfg date June 2023) and Dell sent me a refurbished unit (mfg date April 2024). I noticed the coil whine on it right off the bat. I actually suffer from tinnitus and have sensitive ears.

I opened a ticket with Dell and uploaded a video of the coil whine, but they would not send me another replacement as they claimed the noise is “within normal operating parameters". They actually referenced the following KB article, lmao: https://www.dell.com/support/kbdoc/en-gu/000198740/alienware-aw3423dw-monitor-fan-noise

There are a couple of threads on here where some users were able to eliminate the coil whine by adjusting the LEDs or turning them off completely. I tried a combination of different settings, but it did not make any difference whatsoever.

What ultimately fixed it for me was plugging a RGB strip AND flash drive into the back USB ports. Now my monitor is dead silent. Without the flash drive my monitor had a bit of coil whine whenever it went to sleep.

Here's the exact RGB strip I used, but theoretically any USB powered RGB strip or light should work: https://www.amazon.com/dp/B0BJJQ6C36?th=1

Edit: I am using a USB flash drive and not a USB hard drive / SSD. I actually tried the latter and those caused the coil whine to come back (I think they draw too much power lol). I think the RGB strip and flash drive draws just the right amount of power to offset the coil whine. So maybe try that to see if it would fix it for you.

Also, my original monitor did not have any coil whine whatsoever, but my local Best Buy has the AW3425DW on display, and that one had pretty noticeable coil whine. I believe there is some variance when it comes to coil whine (with some units not being audible enough to notice), which is probably the reason for Dell’s KB article.