My tip would be to claim you don't have a cat on the application and then say you just got it if asked. It's what I've done with my dogs thus far... on the other hand Zürich is one of those cities where every neighbor, janitor and passer-by will stick his/her nose in your business including looking through your windows, watching when you come and go and listening at the door... tough terrain for a newcomer...

As for the noise, yeah... that's gonna be a problem, do yourself and your cat a favor and have him neutered (my opinion without knowing your cat or situation well). There's too many strays around as it is, and it's gotta be torture for him to get the urge and not be able to do anything about it.

Know this is late but maybe someone is interested?

Cheers