A line at 333.324 Hz has been present since the start of the run. I just recently realised that this line is part of a comb in the spectrum with that spacing (see first attachment), and the first six lines of this comb can be seen with SFTs of 1800 s averaged over ~one week of data. The amplitudes of these lines seem to be quite constant over the run.

I found that the line at 333.325 Hz is coherent with some ETMX channels: L1_NOISEMON, L1_MASTER, L3_MASTER, L3_LVESD... These lines are also at the LSC-DARM_OUT, OMC-DCPD_A and OMC-DCPD_B channels, as can be seen in the second attachment.

It is a little bit strange that the second stage L2 is not showing the line, but it could happen if the noise monitors for L2 have a higher noise floor. The line does not appear at any ETMY channels. Since the lines appear in all these channels I couldn't pinpoint where it is coming from, although given its very high Q it seems to be a digital feature.