The Sunnah is to read them silently as this is what the Prophet salla Allahu alaihi wa sallam used to do. This is what all schools of thoughts and all Muslims do.

This Imam of yours is ignorant and he is going against the Sunnah

I want to know, is it Sunnah to offer the last rakah of the Maghrib salah and the last two rakah of the Isha salah silently? This question is raised in my mind because in my hometown, the imaam offers the last rakah of these prayers aloud.