do you have additional package installed from AUR -
According to Arch Wiki - Asus N551 only appears to be fix for getting subwoofer working, but may affect other audio settings
Check Pulseaudio Mixer [
pavucontrol will show audio activity level meter (greyed out if muted)
If pavucontrol shows HDMI set as default playback device, should be drop-down menu to change playback device. can also turn HDMI '“Off” in pavucontrol Configuration tab to force use of only onboard analog
Does pavucontrol show headphones detected as “plugged in” or “unplugged”?