I'm using Pulseaudio. The image is of the Output Devices tab and shows the Port set to Analog Output. This is fine and works great. There's another option called Headphones but if you try and set the Port to Headphones it automatically switches back to Analog Output. This is also fine because I don't want to use that port
The problem is that if the volume increases over 87% it automatically switches to Headphones port, which in turns auto switches back to Analog and back and forth quickly and forever making lots of clicking noises.
Perhaps related to that "Base" marker on the volume control?
No idea here, very strange behavior.