It could be his parents. Minato and Kushina might be trying to communicate with him from the afterlife. They could be sharing family secrets or just giving him words of love and encouragement.
It could be the Sage of Six Paths. Since Naruto has the power of the Nine - Tails and is on a path to becoming a great ninja, the Sage might be trying to communicate with him through voices, guiding him to fulfill some greater destiny.
Well, it could be that Naruto starts hearing the voices of past Hokages. Maybe they're guiding him in some secret mission or giving him advice on how to deal with new threats in the village. For example, the First Hokage's voice might tell him about ancient sealing techniques to use against a powerful enemy.
In this kind of fanfiction, the plot could be that Naruto starts hearing voices due to some dark jutsu used against him. Maybe these voices are from his past enemies, like Orochimaru, whispering in his mind, trying to break his spirit. And Naruto has to struggle to overcome these voices and not let them influence his actions.
Another theme is growth. Naruto's discovery of Sakura's thoughts can lead to his own personal growth. He might become more understanding or empathetic. In some fanfictions, after hearing Sakura, Naruto starts to see her in a new light and tries to be a better friend or potential partner. He might work on his own flaws, like his impulsiveness, in order to be more worthy of her feelings.
Well, without more context about what 'Ben' is from (a movie, a TV show, a book etc.), it's a bit difficult to point out exact fanfics. However, if it's a relatively popular franchise, there are likely to be fan-created stories where a character named Ben hears singing. You might also check relevant fan communities on social media platforms. They often share and discuss good fanfics among themselves.
One possible plot could be that Ben is in a spooky old house and hears singing coming from an unknown source. He then tries to find out who or what is making the sound, and it could lead him on a mysterious adventure.
One popular 'naruto hears sakura fanfiction' is 'A Moment of Understanding'. In this fic, Naruto overhears Sakura's true feelings about their friendship and it changes their dynamic in an interesting way.
One popular 'bellamy hears clarke on the radio fanfic' is 'Radio Silence' which beautifully portrays their connection through the radio transmissions. It has a great build - up of emotions and their relationship development.
Reunion hopes. The idea that hearing her on the radio might lead to their reunion is a big element. It gives Bellamy a new sense of purpose to find her. For example, he might start planning a rescue mission based on the information he gets from the radio transmissions.