Telepathic message to Peter
They're called the Gentlemen. They come to town, steal all the voices of everyone, and take seven human hearts. They need them to survive.
Only way to kill them is the sound of a human scream.
Buffy fought them in Sunnydale and killed them. They have box that holds the voices. We destroy that, we get our voices, someone screams, the Gentlemen die. At least, that's how she did it.