HomePod 2nd generation keeps increasing volume by itself

My HomePod 2nd generation keeps adjusting (increasing) volume by itself several times a day. Happens in the midle of a song. Suddenly there is a second pause and then volume goes up by at least 5 to 10%. Very annoying and makes me jump everytime this happens.

It has been the same with HomePod OS 17 and 18.

Nothing helps, Sound check on or off, moving HomePod around, reset... I can see that others have the same problem.