It is not known if these are already present in the power provided by ENEL, if this is caused by one of our own heavy machines that polutes the power line or that it is some weird aliasing in the DAQ.
Fig 2 shows the spectogram of one of the magnetometers during the last air-conditioning tests, to check if this is related to one of the machines that are switched off (the z-axis is zoomed in to show the weak lines, the 50 Hz is saturating). Fig 3 shows the acoustic noise to indicate the times of the shut-down. No lines disappear, so they are not caused by anything related to the air-conditioning. This plot shows clearly that the lines are side-bands of the 50 Hz, which are visible to at least 3rd order. There are also some lines which are folded in frequency, as if they were side-bands of lines at ~25 and ~75 Hz lines.
