JeffK is going to produce a much more extensive result and possibly conclusions but the simple view is here.  I selected a few chambers to look at BS, ITMX and HAM5.  HAM5 is closest to the Pump Stations, HAM1 is certainly the farthest but it isn't unlocked.  HAM2 might be a better candidate but too late, I chose ITMX, the BS is where the pressure sensors are which derive the differential pressure channels.

I looked at all DOFs (not VP) and we see/saw lots of coherence with HP RZ and Z on most chambers.  HP & RZ being the largest.  I show HP, RZ and the oplev YAW and Pitch of the optic on the platform in the attached plot.  The top group is the BS, the middle traces are HAM5 and SR3, and, the bottom group is the ITMX.

Pretty much nothing seen on the Oplevs but the coherence on the RZ and HP loops when the HEPI Servo is on is pretty clear compared to when the drive to the Pump Stations is fixed ignoring the pressure signals.

More Details:  Switched the Servo to Manual state at 1510utc this morning and made one output tweak at 1514.  The Sensor corrections to the BSCs were turned off at 1549--this may come into the spectra toward the ends of these 10 average 1mHz BW measurements.  The current traces are with the servo off and are started at 1515utc.

The servo was turned back on at 1716utc.  The reference traces (dashed) in the plots where started at this time.

My current conclusion from this is the noisy pressure channels is injecting this noise into the drive signal and it is getting to the platform.  We will tune the controller to help deal with this but the noisy signals must be addressed.