System sounds not-muted, even though I have them set to muted

[nikgnomic]

Disable pcspkr kernel module that creates error beep alerts

sudo rmmod pcspkr

And create a blacklist entry to prevent udev loading it at boot

sudo tee /etc/modprobe.d/nobeep.conf <<< 'blacklist pcspkr'

Disable PC speaker - ArchWiki