NASA has an explanation for the "strange noise" emitted by Boeing Co.'s Starliner spacecraft docked at the International Space Station.

The noise was heard by astronaut Butch Wilmore, who radioed mission control about the sound Saturday, as first reported by Ars Technica. "There's a strange noise coming through the speaker [on Starliner]," he said. "I don't know what's making it ... I don't know if there's something that's maybe connected between here and there making that happen," he added.