Sounds to me like something along the wire from the speaker to whatever it's connected to is acting as an antenna, and the noise sounds like broad-spectrum radio static, the kind you get during a thunderstorm from lightning. But, it's too periodic (anyone want to open it up in Audacity and tell me if it's actually accurately periodic?)
It would be interesting to know what they were over when they heard it. Or is it happening everywhere? Could be they're picking up HAARP or something.
Also, not the first time strange sounds have been picked up in space: https://www.youtube.com/watch?v=UDQ8WK_oR-s