Learn Hardcore Japanese: tonari no heya kara ongaku ga kikoemasu.

It literally means “the neighboring room.” The particle の links 隣 (neighbor/next) and 部屋 (room) in a genitive or attributive way, turning them into “adjacent room.”

Why is から used after 部屋? Could I use で or に instead?

から indicates the origin of something—in this case, the sound is coming “from the next room.”

で marks where an action takes place, not the source of a sound.
に can mark the starting point of physical movement but isn’t used for the origin of a noise.
So when you say “I hear music from the next room,” から is the correct choice.

Why is 音楽が marked with が instead of を?

Because 聞こえる is an intransitive verb meaning “to be audible” or “to be able to hear.” Intransitive verbs take が to mark their subject. Here, 音楽 (music) is what is being heard. If you used the transitive 聞く (“to listen to”), you would say 音楽を聞く.

What’s the difference between 聞く and 聞こえる?

聞く is transitive: “to listen to” or “to hear” (you actively do it, takes を).
聞こえる is intransitive/potential: “to be audible” or “can hear” (describes passive perception, takes が).

Why is there no subject like “I” in the sentence?

Japanese often omits obvious or contextually clear subjects. The speaker’s perspective (“I hear music”) is understood, so 私が (“I”) is left out.

Could I put 隣の部屋から after the verb instead, like 音楽が聞こえます隣の部屋から?

Japanese word order is flexible, but locational/adverbial phrases normally come before the verb.
You could say 音楽が隣の部屋から聞こえます, but it’s more natural to keep 隣の部屋から at the front.