The problem
I have a Pi 2B running Ubuntu MATE connected to a small TV by HDMI. For some reason I get no sound for practically all of the time, neither on HDMI nor the headphone jack, even after forcing the sound output to the relevant device using raspi-config.
Some details and background
One thing that is very interesting about this is that if I leave my Pi alone for a long time while playing audio, the audio improves slowly until is is is almost clean (it sometimes takes hours just to get intermittent snippets). Whenever I start doing things, however, like switching windows or clicking, it immediately goes back to its former state.
Another interesting thing is that the sound has deteriorated from being usable to absolutely useless. At first OMXplayer worked fine, but now nothing works.
I don't have any more clues or ideas to give. I am stumped and frustrated, and I just have to live with non-functioning audio. Anyone who can help me solve this will get a 100 rep bounty.
pulseaudioworks on top of the ALSA system so needs the latter - what the former can do is confuse you but allow sound to be played across a LAN - do you have a pulseaudio installation on a Desktop PC with the same login that the RPi may be swapping audio data with (although I think you have to have shared cookie to do so)? If so it is possible to get loops which hogs your LAN bandwidth and also produces choppy playback and other stuff if things aren't configured correctly. 8-(