Responding to numerous complaints about a low frequency hum the US Government commissioned an investigation into the cause.
The investigation was carried out by the University of New Mexico with the help of the Los Alamos and Sandia National Laboratories.
The investigation was in two parts, part 1 to look for an acoustic cause and part 2 to look for an electromagnetic cause.
The investigation lasted two years and concluded that there was no evidence to indicate that the Hum was caused by sound waves or mechanical vibration.
The electromagnetic part of the investigation was deemed as restricted and the results were never made public.
Using the Freedom of Information Act attempts have been made to see part 2 but these have been refused.