Type in the terminal:
sudo apt-get install pavucontrol
Now start pavucontrol and see how the sliders are positioned. You start pavucontrol from the Quick Finder or from the terminal: simply type in: pavucontrol (and press Enter).
Note: do not open the sliders all at once, and none for more than 90% (distortion)
Possibly choose a different sound profile. To do this, click on the Configuration tab and choose a different profile. E.g. Analog Stereo Output
