The modulation amplitude was raised from 7 dBm (O2) to 12 dBm (Post-O2 Commissioning) on Aug 27 (see entry 42544), as usual between Dark Fringe and LOW_NOISE_1; at the time it resulted in some improvement, today we made the test to reduce it once in LOW_NOISE_3 in order to check it. In the attached plots there is a zoom of both Hrec and DARM in the band of interest, with the following timestamps ( + 180 s) and colormap:

Unfortunately no big change was observed and the pattern is not related to the decrease of the modulation amplitude; the only remark is that at 11 dBm the noise seems quite better; to be checked if this was just a coincidence or if maybe our modulator is less burdened by a slightly lower modulation amplitude.