See JeffK's 16857 where he analyses the End Station's performance relative to the fluid pressure noise.  The attached plots compare those final performance numbers for YEND  from Sunday at 6pm pst with data taken 25 Feb at 0230utc -- after the EndY HEPI plumbing system maintenance detailed in 16899.

Bottom line--The DOFs still showing coherence on Sunday (Jeff's 16857) are all almost completely gone, there is still a bit of coherence in the HP dof in places between 10 & 100mhz.  So this maintenance would appear to be very important.  The DOFs remaining were the 'common' mode dofs.  That is, the Z and the HP modes of the HEPI--those dofs where the Actuators move in common.  All other dofs have counter moving actuators which one might expect a common noise like pump pressure to cancel out.

Now, understand, Jeff's work on the controller characterization and tuning provided most of the decoupling to the platform; this maintenance work just closed a few final loose ends.

The xml for these is /ligo/svncommon/SeiSVN/seismic/HEPI/H1/Common/2015-02-25_H1HPI_EndYStation_Coh_wISIT240s.xml