Improve sound insulation of interior walls and ceiling

What a nice interaction here, a mirror of society

Of course it is acknowledged here when someone lightens the technical discussions so humorously by putting heavy stones in a wooden house.

Especially since I do not understand a house made by a carpenter and a prefab house construction expert

You have so far written about timber frame construction without any indication of a unique piece. But whether it is industrial or not, the construction method remains the same. And from my point of view, the prefab house expert is a top choice as an expert to diagnose and recommend therapy concerning the causes and suitable remedies for the perceived defects. Who else? (as said, I would have also recommended the colleague Zink here, if you were not in SH and he in BY).