This sound was produced by William Sturridge in December. It is from a spectrum analyzer amplified to the audible range. It came across at 60 Hz. The beat tone that sounds similar to a pair of diesel engines that are not synchronized suggests power in the grid not being timed. This will create harmonics above and below 60 Hz, and those below the hearing threshold are, according to Sturridge, dangerous. The sound was recorded by two microphones attached to an ASUS laptop and fed through a Pioneer amp.