NASA astronaut Butch Wilmore reports 'strange noise' coming from Boeing's Starliner spacecraft, 'I don't know what's making it' 

 The eerie sound was likened to a pulsing sonar-like ping. 

https://cdn.mos.cms.futurecdn.net/vJceQ6bFjKXScohvm73vZ5.jpg

https://www.space.com/strange-noise-boeing-starliner-spacecraft