Figure 1 compares magnetic noise in the central building during VSR4 and now when most devices are off. Despite the significant reduction of noise. Yet a few intense bump structures remains apparently unchanged: the first at 14Hz and then as +-14Hz sidebands of 50Hz and multiples. The same magnetic noise is  also present at WE and NE (Figure 2 is for WE). also the frequency is very stable with time (Figure 3). The origin is not understood. Some coherence is found with IPS probes (Figure 4), but the intensity is very low, which might indicate this is the effect of  some magnetic noise pick-up of the IPS sniffer probes.

The 14Hz frequency roughly corresponds to the frequency of one of the Schumann's EM resonances of Earth's ionosphere. However this seems not the case: the noise seems not present in the outdoor magnetic spectra we took in two occasions: near CB with the flux-gate magnetometer, and at further distances with the same MFS-06 low noise magnetometer in use inside buildings. Also note, noise peaks are NOT coherent among distant magnetometers, like NE and WE (Figure 4).