This is regarding the excess noise at LHO mostly in 20-40 Hz band that I discussed earlier in the alog 71214. In the Q scans, this noise appears as “scratches” mostly between 20-40 Hz band. As mentioned in this alog, these scratches are separated by ~ 0.2 seconds, which would correspond to 1/(2*0.2) or 2.5 Hz motion upconverted to 20-40 Hz band. This noise started getting worse around June 22 when LHO moved to lower power. This change resulted in improved sensitivity at lower frequencies, and this can partly explain the increased visibility of this 20-40 noise in DARM. 

I also noticed that there is a peak at 2.55 Hz in HEPI Y and Ground Y that shows up on June 17 (barely visible) gets stronger between June 17 and June 22 and has been present everyday since then. This peak is visible in most HAMS, here’s HAM6. There is another peak at 1 Hz that appeared on June 21 and has been present every since. 

The appearance of this 2.55 Hz peak could be the second factor responsible for the increase in noise June 22 onwards. However, this doesn’t explain why this noise is present in the data prior to June 22 (albeit with a smaller rate).