Is there a word (in any language) for the sounds you "hear" (imagine) when listening to something? ?

E.G., you're listening to a song, and you "hear" a harmony (not a harmonic) that would fit well, but isn't actually part of the song. Maybe something like synesthesia, but only involving sound...(Synesthesia involves a "cross-wiring" of the senses, so to speak... I believe this activity is something everyone does, or at least the vast majority of musically inclined people...)