Are you sure it is PulseAudio? In case of multiple outputs (headphones, speakers), PulseAudio can change volumes of them based on data from ALSA. Intention is t

Are you sure it is PulseAudio? In case of multiple outputs (headphones, speakers), PulseAudio can change volumes of them based on data from ALSA. Intention is that volume stays the same, except if the data from ALSA is wrong. Even with one output wrong info from ALSA will result in sudden volume changes.