I kept getting this odd issue when using the latest Fabulously Optimized modpack.
My audio would start randomly making this low electric whine sound around startup time and never go away.
I eventually found that setting my max FPS back to 120 made it go away, but the pack's default 260 and the Unlimited option in game seem to make it come back.

I had to install the mod pack and then disable Dynamic FPS before starting the first time, then it would function just fine.
The modpack version is "6.5.0-beta.7-mr.1" which is for 1.21.4
The version of Dynamic FPS being used in it currently is 3.9.0 (dynamic-fps-3.9.0+minecraft-1.21.2-fabric.jar)
I installed that modpack through the latest version of prism launcher.

I'm not entirely sure if my speakers are to blame or not though.
My speakers are Sony VAIO VGP-SP3 and the side without volume controls is non-functional.
They are two separate speakers connected together that plug into the PC if you can't find images (Should be able to).
I've had them a long time though and haven't seen this issue elsewhere.

Here's my system specs:
CPU: AMD Ryzen 7 5700G
GPU: EVGA RTX 3070 Ti 8GB
RAM: 2x 16GB 3600MHz GSkill Ripjaws (XMP profile is default I think?) (32GB total)
Drive: Samsung SSD 970 EVO Plus 2TB (NVME M.2)
OS: Windows 10 Pro (Same bug happens on Linux Mint 22.1 I used in dual boot)
GPU Drivers: NVIDIA 572.70 (Game Ready) (Just Installed)

Here is my system summary:
msinfo.txt

Edit Combine Small Comments into one post:
The sound seems to change slightly in different menus

I just tested mono output in windows 10 ease of access settings to make sure it wasn't sure weird channel thing
It still acts the same in that case

I don't seem to get the bug when tested in isolation and with the latest sodium installed.
Not sure why this happens in that modpack with this mod enabled

Ah but it does do this in isolation when you disable all other mods in the modpack.
Could be a configuration change then is my first guess
No that may have just been something cached from the last run, weird that it does that.
On a fresh install of the modpack with all mods and resourcepacks except for "Fabric API" and "Dynamic FPS" enabled, it won't happen. Options did get set to 120 max fps but I set it to unlimited and it didn't happen here, it's odd.

If I install fresh install of the modpack and disable "Dynamic FPS" before running it, the bug goes away.

Hello, this is indeed a bug that cropped up in 1.21.2+.
Certain configurations cause no frame rate limit to be applied while on the main menu.

However, I should note that having coil whine is pretty normal when any application runs at a too-high frame rate, so even with this bug fixed you might run into this while playing without a frame rate limit (I have this issue as well when using the default configuration of this modpack, since it consistently runs at 500+ FPS on my computer for no good reason).

This has now been resolved in v3.9.1.

The bug still happens in game while paused
It appears fixed in the title screen

Not sure if thats something that can't be fixed or not
It carries over to the gameplay slightly after but is more prevalent in the pause screen
If I open the F3 menu while unpaused it seems to stop after a second

In theory it could, but reducing FPS while on the pause screen is not a feature the mod has at this time.
What you should really do is set a frame rate limit in the game's regular options (even if you just set it to 250), or do you actually have a display that can show more? It's kind of just a waste of energy.

My display is the AOC CU34G3S which is a 3440x1440 165hz curved 21:9 ultrawide monitor
It can't really take advantage of the super high FPS but I was wondering if it was a bug that should be addressed anyways

If I plug my speakers into my monitor directly it seems to fix the coil whine
Though they at all times (even out of game) have a tiny buzz that might bother me lol
So I may plug them back into PC

I see :) Not a bug, but you could create a new issue as a feature request, though I will not get to it as fast.