Learn Hardcore Portuguese (Brazil): Meu vizinho é barulhento durante a noite.

In Brazilian Portuguese, it’s common to drop the definite article before a possessive adjective (like meu, seu, nosso). So meu vizinho is perfectly natural. You can also say o meu vizinho without changing the meaning, but omitting o is more idiomatic in Brazil.

Why do we say durante a noite instead of na noite or à noite?

durante means “throughout” or “during,” emphasizing that the noise happens over the course of the entire night.
na noite literally means “in the night,” less focused on duration.
à noite means “at night,” a general time reference (e.g., “I study at night”).
All three are grammatically correct, but durante a noite stresses that your neighbor is noisy through the night.

What is the role of the a in durante a noite?

That a is the definite article “the” in English. Portuguese requires durante to be followed by the article: durante o dia, durante a manhã, durante a noite. You can’t drop it after durante.

Why is the verb é (ser) used instead of (estar)?