Tagging ISC, PEM, and DetChar -- this is a follow-up action taken now that we've found that the detector is particularly sensitivity to scattered light from the ETMX cryo baffle; see LHO aLOGs 69598 from Evan, and 69603, Andy's ID that it may be this fan that Bubba has now turned off as indicated in the above aLOG. The game plan: since improving the isolation / damping of the cryo baffle would require an end-station vent which we're not willing to do, we're instead looking to reduce the input motion to the cryo baffle's isolation system. 

Last night after this change, the detector was left in observing mode for roughly 9 hours. This data that does not contain any visible 4 Hz glitching (see attached spectrogram). Additional checks of data during daytime hours would be helpful to confirm that the 4 Hz glitching is no longer an issue, but this is a promising sign.