Maybe not common, but not rare either.
I had sound hiccups on two systems when transitioned from 2.6.X to around 3.1 kernel.
In one case I selected the correct 5.1 sound but only got stereo until I powered down (reboot wasn't sufficient).
So as a start there are two tools,
Use 'pavucontrol' and in the configuration tab select the correct hardware proflie ... probbaly "Digital Stereo (HDMI) Output" ,and also adjust the output balance and volume. Sometimes hter eis more than one HDIM output to choose between.
Also in a terminal window use 'alsacontrol' . It's a crufty little terminal graphics tool, but it does give you acces to all the mutes and volumes.
HDMI is not a problem per se - I've used HDMI audio on two systems.
yum -y install pavucontrol alsa-utils
---------- Post added at 07:22 AM ---------- Previous post was at 07:14 AM ----------
Editing /etc/fstab isn't rocket science, but it must be done correctly.
You might want to try 'fwfstab'
yum - y install fwfstab
It's a gui tool for editing /etc/fstab that at least avoids the hazard of a mis-edit, and ensues al lthe fields are fille in.