[ericq, gautam]

We poked around trying to figure out the X PDH situation. In brief, the glitchiness comes and goes, not sure what causes it. Tried temp servo on/off and flow bench fan on/off. Gautam placed a PD to pick off the pre-doubler AUX X IR light to see if there is some intermittant intensity fluctuation overnight. During non-glitchy times, ALSX noise profile doesn't look too crazy, but some new peak around 80Hz and somewhat elevated noise compared to historical levels above 100Hz. It's all coherent with the PDH control up there though, and still looks like smooth frequency noise...

NB: The IR intensity monitoring PD is temporarily using the high gain Transmon PD ADC channel, and is thus the source of the signal at C1:LSC-TRY_OUT_DQ. If you want to IR lock the X arm, you must change the transmon PD triggering to use the QPD.