During several scenes on Lost, the show's main characters would be shown running through the jungle when they would suddenly hear strange and mysterious whispers all around them. In its earliest seasons, the whispers came off as creepy and spooky, especially since so much about the island was still a secret at this point. After the Others were introduced, it was believed that they were the source of the whispers -- but this was not the case.
In Lost season 1, Sayid (Naveen Andrews) encountered the French woman for the first time. He didn't believe her when she told him about the whispers she heard when her baby was taken by the Others. Sayid came to a horrifying realization when after a run through the jungle, he too heard the whispers. For many, it was one of the creepiest moments in the series. Other characters on the show, such as Jack (Michael Fox), Kate (Evangeline Lilly), Sawyer (Josh Holloway), Shannon (Maggie Grace), and more have had their own eerie encounters with the whispers.
This is one of the few island mysteries on Lost that at least seemed to have an obvious explanation. Nearly every encounter with the whispers was in some way tied to the Others, the mysterious group that inhabited the island. On numerous occasions, the whispers would be heard shortly before one or more of the Others would make an entrance. This mystery went unexplained until season 6. Shortly before the Lost series finale, Hurley (Jorge Garcia), who has the ability to communicate directly with dead people, was confronted by the spirit of Michael (Harold Perrineau), who died at the end of season 4. Michael told Hurley that the whispers are actually the voices of people who died and were trapped on the island, unable to move on.
So what's the connection between the whispers and the Others? It seems likely that the ghosts were trying to warn the survivors that the Others were coming. It may be that some of the whispers were from members of Lost's Dharma Initiative, who were massacred decades ago by the Others in an event called "The Purge".
The true nature of the whispers was hinted at way back in season 1, when Sawyer believed that he heard one of them say the phrase, "it'll come back around", which was said to him by a person he murdered off the island. Sawyer never found out if the man's ghost was haunting him, and even now, after the mystery's been explained, it's still not clear. There have been other instances where the ghosts have whispered phrases that register some sort of meaning to the characters. Though they mostly seem like unintelligible noises, it is actual dialogue that's been layered on top of each other, and transcripts of the whispers and what they're really saying do exist. Even so, the meaning behind their words is open to interpretation. The ambiguous nature of it all, combined with the creepy vibe given off the whispers, helps make this one of Lost's most compelling mysteries.