Music of the Ainur: Rap? Country? Opera?

[Ithaeliel]

I always thought the drums were supposed to be the footfalls of the balrog in Moria, but then there was this passage:

They looked back. Dark yawned the archway of the Gates under the mountain-shadow. Faint and far beneath rolled the slow drum-beats: doom.

So I'm somewhat confused as to what the drums were. But I'm off the topic. The music of the Ainur I imagined to be voices that sounded similar to orchestral instruments, and they sang together in harmony. Then Morgoth made a different theme, and they sort of fought with each other: there was a dissonance, maybe sort of like a canon. I imagine it to be medieval as well.