By comparing the acoustic injection inside the DET lab with that we routinely do inside the CEB hall (loudspeakers on DE Tterrace) it is evident a difference in the excited Hrec peaks: when injecting inside the DET Lab no structure in hrec is excited (just barely a peak at 502Hz) - see Figure 1 - while when injecting with loudspeakers in the Hall a number of peaks arise - see Figure 2. Frequencies are: 502, 460, 469, 412, 383, 371, 278, 203, 172 Hz. 

Figures 1 and 2 compare the injected noise levels of microphone in the hall and inside the DET lab and one accelerometer on SDB1 vacuum chamber. We deduce that acoustic noise inside the DET Lab is not the driver for these peaks. The Vibration noise of the SDB1 is larger (roughly a factor 2 or 3) when injecting from the Hall, so SDB1 chamber vibration might be a suspected path. However, comparing with peaks excited with tappings on SDB1 chamber and viewports/mini-links (done in 2023) we do not find a good match, except for the 502Hz and 172 Hz: https://logbook.virgo-gw.eu/virgo/?r=62759, https://logbook.virgo-gw.eu/virgo/?r=62796.

Preliminary conclusion: the excitation path of these peaks is not clear, and would need further investigation.