Sept. 2 Update: NASA issued the following explanation on Monday for the strange noises: "A pulsing sound from a speaker in Boeing’s Starliner spacecraft heard by NASA astronaut Butch Wilmore aboard the International Space Station has stopped. The feedback from the speaker was the result of an audio configuration between the space station and Starliner. The space station audio system is complex, allowing multiple spacecraft and modules to be interconnected, and it is common to experience noise and feedback."
That's a cop-out, not an explanation. It's not like anyone expected new physics or ET to be the explanation; of course it was going to be some interaction of complicated systems.
A previous discussion of the Ars Technica article which embeds a player for this clip:
When that topic was first posted; I seriously thought that it was a joke post, refering to Star Trek IV when the probe was nearing earth, making what turned out to be whale sound but sounded like that.