Wrong! You must check with your landlords and get permission in writing. This is written into all of the rental agreements that I have had in the Zurich area. When I originally approached my landlords to teach guitar they refused permission. After some negotiation with them I am now able to teach for a few hours each day within set times, dependant on all of the neighbours consenting. My music room is 2 floors away from my nearest neighbour and in a half-commercial building, and I still had problems.

I have a neighbour who is a piano teacher who also has restrictions (not during lunch or after 7pm etc) and she has taught successfully now for over 15 years from her home, within these rules.

Check your rental agreement. If it mentions musikunterricht then do not ignore what it says or you will potentially be looking for a new home.