An apparent 10-Hz comb at 1028, 1038, 1048... Hz was spotted while updating the lines lists. The peaks are right on integer frequencies (to within a single bin in 7200s SFTs).

I took a closer look and found that it's actually a single line jumping around in the spectrum. Anybody recognize this?

The line can also be seen in H1:PEM-CS_MAG_EBAY_LSCRACK_Z_DQ. It seems like it started coupling to DARM after the O4a/b break.

Details:

History of the line in DARM:

• 1028 Hz from 2024-03-23 through 2024-03-25
• 1058 Hz from 2024-03-26 through 2024-09-05
• 1028 Hz from 2024-09-06 through 2024-10-21
• 1038 Hz from 2024-10-22 through 2024-11-27
• 1048 Hz from 2024-11-27 through 2025-03-24
• 1068 Hz from 2025-03-25 through 2025-03-27
• 1058 Hz from 2025-03-28 through 2025-04-01

Comparison of magnetometer and strain data (y-axis for all plots is frequency; label got cut off for some reason): 

• Figures 1 and 2 show a narrow region around the 1028 Hz line. Figure 3 shows a zoom in on the early March 2024 strain plot, which is otherwise hard to see. Figures 3 and 4 show a narrow region around the 1058 Hz line.
• Interpretation: Figures 1-3 demonstrate that the line was visible in the magnetometer channel, but not in DARM, prior to March 2024. All four figures show that the artifact in DARM matches that in the magnetometer channel after March 2024.