It could be the muffled sound of someone singing in the shower or that nonsensical, indecipherable speech of the Muppets' Swedish Chef. In fact, the bizarre audio unveiled by scientists on Monday is that of a beluga whale imitating the voices of people. In fact, the whale's song sounded so eerily human that divers initially thought it was a human voice. Handlers at the US National Marine Mammal Foundation in San Diego heard mumbling in 1984 coming from a tank containing whales and dolphins that sounded like two people chatting far away. It wasn't until one day, after a diver surfaced from the tank and asked, "Who told me to get out?" did researchers realise the garble came from a captive male beluga whale named Noc. For several years, they recorded the white whale's spontaneous sounds while it was underwater and when it surfaced. An acoustic analysis revealed the human-like sounds were several octaves lower than typical whale calls. The research was published online Monday in Current Biology . Scientists think the whale's close proximity to people allowed it to listen to and mimic human conversation. It did so by changing the pressure in its nasal cavities. After four years of copying people, it went back to sounding like a whale, emitting high-pitched noises. Noc died five years ago. Dolphins and parrots have been taught to mimic the patterns of human speech, but it's rare for an animal to do it spontaneously. The case revealed in the study is not the first time a whale has sounded human. Scientists who have studied sounds of beluga whales in the wild sometimes heard what sounded like shouting children. Caretakers at the Vancouver Aquarium in Canada previously said they heard one of their beluga whales say its name.