I got an amp to plug into the audio and was struggling to work out why sound was only coming out of one speaker (left) then I by chance and changing every setting I could found the issue was in the ASUS Realtek HD Audio Manager there was an 'Amplifier' setting and it was set to 'Front Panel' and changing it to 'Auto Switch' cured the problem! Amazing. So full disclosure I have a very old machine with a Z170-AR motherboard in it.
