There is a bump disturbance in the H1 strain spectrum that is degrading the noise in the vicinity of the Crab pulsar. Attached are zoomed-in ASDs from recent dates (drawn from this CW figure of merit site). That band was pretty stable in O4a, but has been unstable in O4b. I can see hints of the bump as early as the end of March 2024 (see calendar navigation to sample dates).

I have poked around in Fscan plots and tried the handy-dandy Carleton coherence mining tool, but saw no obvious culprit PEM channels. Is there a new motor running somewhere (or an old motor with a drifting frequency)? 

Attachments:

Sample ASD snippets from August 1, September 1 & 2, along with a snippet from the end of O4a on January 16.

The red curve is from one day of averaging, and the black curve is the run-average up to that date.

The vertical bars show the approximate band of the Crab pulsar during the O4 run (taking into account Doppler modulations and long-term spin down).