This entry comes a bit late, since our crew has already spotted it and is working to reduce frequency noise. However.... as Figure 1 shows, there is significant coherence between DARM and SSFS in the region 20-100Hz.

The rightmost of the 30Hz double-peak structure is associated to frequency noise: this is precisely at 30.8Hz, and matches to a peak in the SIB1 angular signals particularly intense in tz: see Figure 2. This peak is also coherent with ENV accelerometers on IB as indicated by bruco.  This peak seems one of the SIB1 mechanical resonance which was troubling SSFS in January.  Reminder: the leftmost one of the double-peak, at 29.8Hz, is not coherent with SSFS and has been found to come from SDB1. 

A structure similar to the 30.8Hz is present at 62.5Hz, probably another SIB1 tz mode: see Figure 3.

Last to note among SSFS contaminations (look again Figure 1) is the 1Hz comb showing between 40Hz and 50Hz. It is not coherent with *Clocks* but with CEB magnetometers and power line sniffers. The suspected source is the CT heaters. It looks the same which was noted in February and March.