Detecting location of infrasound noise in a building
I had a similar problem in a university I worked at.  We used a seismic accelerator, a preamplifier, and a laptop.  We tracked the noise down to the chillers on the roof, when both compressors were running they sent a 100hz signal with low amplitude straight through the building like a huge tuning fork.  Changing the dampening springs and adding other dampening media removed the symptoms in the end