DigiMelody

A DigiMelody (デジメロディー) is a short piece of music that represents a Digimon's data.

Digimon Fusion
DigiMelodies appear to be produced by Digimon who are fading away and can come in various colors. Mikey Kudo is able to hear DigiMelodies, which other humans don't seem to be able to.

After witnessing strange events happening in Kōtō Mikey hears the DigiMelody of a dying and is able to communicate with him. He later hears the DigiMelody of after he is cast out from the Sweet Zone.

After returning to the Human World Mikey, Jeremy Tsurgi, and Angie Hinomoto discover in the same place they met Shoutmon. Omnimon tells them about the history of the, and that he wanted to find a person who would be capable of listening to the cries of the Digimon's DigiMelody and come to answer them.

When facing, Shoutmon and hear 's DigiMelody.

While inside, Mikey hears Shoutmon's DigiMelody again right before he saves the boy from MegaDarknessBagramon's attack.

Digimon Xros Wars (manga)
Mikey hears the DigiMelody of an injured and is able to communicate with him.