Why does button emit a buzzer sound and how can I deactivate it?

The buzzer is a signal to show you, which type of click (short, long, very long, double) you have used. Your button emits a short sound in case of a short click, a very long tone in case of a very long click and so on. You can practice how the click types differentiate with the INFO control button in the elements App.
If you want to turn off the buzzer you have to select your button in the SYSTEM OVERVIEW. Click on EDIT and deactivate it under BUZZER. The sensors LED still indicates which type of click you have used at the moment.

After you have turned the buzzer off - please press the button. You will hear the tone but the next time you click it the tone is gone. This is as the button needs the connection to your phone to get the order to "turn of buzzer" and than it works.

So. Open System overview - turn off buzzer - click button once (with tone) click button again (not tone) . Same occurs the other way around