Wdym? I think that the inner monologue is "hearing it", with a varying degree of vividness between people, of course.
I don't know how much this style of thought came about because I really didn't enjoy constantly visualizing things and consistently fought against it; mainly due to the constant intrusive visual sequences of various types, of which I still have far too many for my taste. I use schematic and visual imaginations all the time, but I guess I feel safer using the monologue and so it has become the bulk of my thought. At the same time the fact that I have learned several languages and have had to consciously focus on language over the years undoubtedly plays a big part. I wonder how many polyglots who learned languages later in life use a similar monologic imagination style?
My monologue uses several languages... But my monologue has always been there, since years before I learnt my second language.
I can think about a song, think about the melody, lyrics, etc… but I don’t hear it. If I hear a couple notes that remind me of a song, I can go through the rest of the intro, get to where the lyrics start, and get to the chorus and remember the name of the song (if it doesn’t come to me instantly), but it’s nothing like playback. It’s more like my inner monologue doing a bad a cappella cover version.
I sometimes wonder if everyone is talking about the same thing, but using different language to describe it. Some being more vivid and metaphorical in their speech than others.
As someone who can hear music "on demand" in my head I can say that's not the case. I can hear the music with instruments and the original singer's voice. It's not as clear as listening to actual music, and in some cases it may be incomplete if I havent' listened to the song for a while, but it's definitely a playback.
As an example, right now I am thinking of The Trooper by Iron Maiden, and I can hear the drums, base, guitars and the lead singer's own voice. I can also separate the different instruments if I want to listen to just the guitar or the singer's voice because I know the song well. I can also change the lyrics or the guitar solo if I want.
It's the same as imagining an image. It is not a perfect reproduction of a "photo" that pops up in my mind, but it is still an image with colours, shapes and faces.
I understand where you are coming from, because you don't have the necessary context. When I read about people who "see" music in colours or smells, or even simple colour blindness, it is hard to imagine. But I still accept that it exists
A percussionist takes a day off and decides to see one of his orchestra's performances. The next day he's back and talking to one of the other percussionists. "How was it?" the other one asks.
"Unbelievable! You know the part where we go buhm buhm buhm buhm?"
"Yeah?"
"Well guess what the rest of the orchestra is doing?"
hums a spirited rendition of the William Tell Overture!