No sound fix
When sound doesn't work in chrome with HTML5 or in flash videos then it can be some of outdated or damaged files that causes the problem. The
pacman -Syyu doesn't help always but it is possible to use a dirty method to updated or reinstall files.
A dirty method to fix problems with packages that might help to fix a numerous of other problems too:
pacman -Qq > /tmp/filenames.list while read FileNames;do pacman --noconfirm -S $FileNames;done < /tmp/filenames.list; reboot
Or just use this to reinstall all packages :
pacman -Qenq | pacman -S -
Other good to know configuration for AUR related packages
SRCDEST="/home/username/AUR/sources-aur" environment variable for storage destination of the source packages.
~/.config/aurgetrc a lot of settings. See also