rpi 3b increase volume by itself

[avk17]

Hellow. I have raspberry 3b and ubuntu mate on it. It is working as internet radio stream player. Sometimes (may be two times a week) rspi increas its volume for 5-10 minutes and then set it to normal level. Alsamixer is always set in 100% and its level never changes. audio_pwm_mode is set in 2. Could it be power or internal linux problems? I have no any ideas.

[epoch1970]

Not likely.
Are you sure nothing (no one) is fiddling with software volume?

[avk17]

i am not shure in software so i check all the way.

[epoch1970]

You can have 2 (or more) volume controls in series. You might be looking at the wrong one.