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.
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.