A new line at 29.96944 Hz appeared the 5 May. I ran a bruco analysis and besides some other channels, it showed coherence with some squeezer channels like OPO_SERVO_SLOW_OUT_DQ.

After running some spectrograms around that time, I saw that this line also appeared in many other channels since a long time ago, but the time it went on in DARM was coincident with the time when it also appeared for the first time in that squeezer channel. That time seems to be coincident with some SDF changes reported here, which changed some settings in two squeezer channels.

The attached image shows a comparison of the spectra before this SDF changes and afterwards, where the new line can be clearly seen.