For the brief period that we were locked at NLN today we noticed the 32 Hz line in DARM was much larger than before. I happened to have a HAM shaking template open and noticed that the line was also seen in sensors in HAMs 2 and 3 (first attachment).

Looking at the time series, there has periodically been extra noise in both HAM ISIs since ~last Wednesday (second attachment).

Dan noticed that a noise with the same periodicity is seen in the anthrogogenic band ground motion FOM, in the corner stations z axis (third attachment).

Does anyone know what this noise is?