NOTE: I've solved this issue on my end. See "Solution" below!

Problem
I was experiencing unbearable audio crackling / buzzing on windows 10 desktop version of PICO-8 v0.2.0I
However, I was not experiencing this crackling in the web player.

Here is a clip of what it sounded using the music from the Tetraminis Deffect cart.
https://cdn.discordapp.com/attachments/215268097441923075/726808638941036554/Tetraminis-Deffect-win10.wav

User "kometbomb" on the PICO-8 Discord pointed out that it looks like the signal is getting set to 0 repeatedly.

I tried changing the "mix_buffer_size" value in the config to 2048, but it did not appear to make a difference.

Solution
My audio interface was set to 24bit 44100Hz through Windows' sound settings, and changing this setting to 16bit 44100Hz resolved the issue.

However, I changed the setting back to 24bit 44100Hz, and I was still not having this issue anymore.
Looking back at the screenshots that I posted in the Discord, I saw that my Scarlett 2i2 was somehow set to 8 channel 24 bit, 44100Hz, even though the 2i2 only supports 2 channels.

Specs:
GPU: 1070 TI
CPU: Ryzen 5 2600
Audio interface: Focusrite Scarlett 2i2 1st gen