I am very disturbed by this loud beeping. It sounds so extreme that everyone not only in the near but also in the far surroundings must hear it.
And now I have started looking for the piezo element. I don't dare cut it off the circuit board because I think the risk of disturbing the electronics is too great. So I covered it with a rubber glue on top. Now the sound is so quiet that it can be compared to a small hornet. That is acceptable.