Siren calls was the name given by the Mayweather family to the strange sounds created by the intense magnetic fields of gas giants. Whenever the ECS Horizon passed near a gas giant, Captain Mayweather would broadcast the siren calls through the ship's speakers. Travis Mayweather claimed that the unusual noises gave him nightmares.
In 2151, when Enterprise NX-01 launched a probe into the atmosphere of a class 9 gas giant, it relayed the siren calls to the ship. (ENT: "Sleeping Dogs")