About the 44Hz: I can add that this same was present also in VSR3 (27553). So we can at least exclude recent additions like the Chrocc. I add that there is also a bit coherence at its harmonic, around 88Hz. I considered if this could be again fans in the CD crate (Suppression of 44Hz and 88Hz bumps) but I would say no. In fact, differently from that case (see 23483) now the dark fringe noise is coherent with magnetic probes and not coherent (or very tiny) with the mirror coils current. Now the signal is very well visible in fixed magnetometers spectra, indicating for some intense source (a fan?) which might couple noise directly to mirror magnets. We can do some hunting with portable magnetic probes.