Warning about missing etc/pulse/default.pa.d/ is not an error
Autospawning is usually disabled by default in Manjaro so it does not interfere with pulseaudio.socket and pulseaudio.service.
If you want to run PulseAudio the old-school way (as a standalone daemon with autospawning)
systemd units pulseaudio.service and pulseaudio.socket should be disabled and masked
Status response from systemd units appears exactly as expected pulseaudio.service is shown as ‘disabled’ because it is under control of pulseaudio.socket
and is shown as active (running) with no error messages
When initramfs are being rebuilt after a kernel update, you might get warnings:
==> WARNING: Possibly missing firmware for module: ‘module_name’
If these messages appear when generating a default initramfs image, then, as the warning says, installing additional firmware may be required. Most common firmware files can be acquired by installing the linux-firmware package. For other packages providing firmware see the table below or try searching for the module name in the official repositories or AUR.
Otherwise, if the messages only appear when generating the fallback initramfs image you have the following options:
You can safely ignore the warnings, if you know that you do not use the affected hardware.
If you want to suppress the warnings, you can install the missing firmware. The meta-package mkinitcpio-firmwareAUR contains most optional firmwares. Alternatively, manually install the needed packages
If you want to get rid of the warnings, but do not want to waste your system space on unneeded firmware packages, you can disable fallback initramfs generation altogether:
Warning: Disabling fallback initramfs generation will deprive you of another option to boot into the system in case a default initramfs fails. Before proceeding, make sure you have a bootable installation medium for rescue purposes on hand.