The following is a Reuters articles I took from online a couple of years ago. I no longer have the link and it probably wouldn''t work anyway:

WASHINGTON, Sept. 9 — Big black holes sing bass. One particularly monstrous black hole has probably been humming B-flat for billions of years, but at a pitch no human could hear, let alone sing, astronomers said Tuesday. "The intensity of the sound is comparable to human speech," said Andrew Fabian of the Institute of Astronomy at Cambridge, England. But the pitch of the sound is about 57 octaves below the middle C at the middle of a standard piano keyboard.

This is far, far deeper than humans can hear, the researchers said, and they believe it is the deepest note ever detected in the universe.

The sound is emanating from the Perseus Cluster, a giant clump of galaxies 250 million light-years from Earth. A light-year is about 6 trillion miles (10 trillion kilometers), the distance light travels in a year.

Fabian and his colleagues used NASA's orbiting Chandra X-Ray Observatory to investigate X-rays coming from the cluster's heart. Researchers presumed that a supermassive black hole, with perhaps 2.5 billion times the mass of our sun, lay there, and the activity around the center bolstered this assumption.