The Hush
From Tardis Wiki, the free Doctor Who reference
The Hush was a weapon built to destroy anything that made sound. It was originally used in war, but since it was attracted by sound, it got into Radio Bravo because the transmitter was beaming its signal in the wrong direction. It had no physical appearance, according to the Tenth Doctor. Possibly created by the Time Lords as alluded to by The Doctor. (AG: Dead Air)
