Comment 98 for bug 1784485

The problem can been solved by updating to the newest 4.19.x kernel. I am a Ubuntu user with Asus UX433FA. After a few testing, I can confirm that newer kernel 4.19.17 currently available in kernel.org is the solution (I tried out 4.19.8 as well but I experienced something else so I decided to use 4.19.17, which, by default, accepts the changes suggested by Jian-Hong).

However, I am using a dual boot system. There is a minor problem that bugs me: even if I turned off the fast boosting in BIOS, if I boot into Windows then restart and try to boot into Ubuntu, the sound will distort and disappear eventually. The solution would be completely shutdown Windows every time you want to switch between the OS. Hope this could be solved in the future.

A good thing though, is after installing the new kernel, the original 4.15.x kernel that ships with Ubuntu 18.04 can also output sound properly !!!

But, I have always got the feeling that the sound quality on Ubuntu is not as good as that of Windows. I might be over-sensitive tho.