Here's a recording of what my audio output sounds like. I am using a USB sound card identified as C-Media Electronics, Inc. CM106 Like Sound Device which is outputed over optical SPDIF to a Denon 5.1 receiver. In Windows, I have no issues with the audio. Under Ubuntu 16.04 there's a constant clicking/popping which is louder as the sound is louder.
I visited other posts and followed a few suggestions like installing pulse audio, changing mixer settings, and other attempts but it still continues. It doesn't happen over HDMI or analog.
Best Answer
Had same problem on megeia 6, found it to be a sample-rate problem. Adding default-sample-rate = 48000 to /etc/pulse/daemon.conf fixed it for me. pulse needs to restart after. pulseaudio -k, pulseaudio --start