The rumblings of a black hole in the Perseus galaxy is 57 octaves below middle C. For comparison, a typical piano has 7 octaves. The Chandra X-Ray Observatory was used by NASA in the discovery of the black hole in 2003. The black hole they recorded is 250 million light years away from Earth.
It was the first time sound waves were found around a supermassive black hole. It supports the theory that black holes are not 'holes' but rather really dense concentrations of matter.
The soundwaves found may actually solve a longstanding astrophysics problem. Scientists have always wondered why they always found pockets of hot gas in the Universe, but almost never cold gas. They think that the sound waves emanating from the black hole cause the gas to remain hot.