Here's a BruCo scan for last night: https://ldas-jobs.ligo-wa.caltech.edu/~gabriele.vajente/bruco_1395660903_GDS_CALIB/ using GDS-CALIB_STRAIN_CLEAN

Some observations on the low frequency range (<50 Hz):

1. there is coherence with PRCL, MICH and SRCL. My guess is that PRCL couples through MICH and SRCL, since there is some coherence MICH vs PRCL and SRCL vs PRCL.
2. however, similar coherence pattern is visible with REFL_RIN, and I'm not sure what to make of that
3. there is coherence with CHARD_Y and lower with DHARD_Y. There is also coherence with HAM1 motion, that's probably due to the known HAM1 to CHARD coupling
4. below 20 Hz it looks like there is high coherence with IMC angular yaw signals, so maybe we're limited by low frequency jitter there?

It looks like we could try to improve the low frequency by:

1. doing A2L again to fix CHARD_Y
2. see if that improves PRCL coherence, if not
3. redo MICH FF and SRCL FF, hopefully that will reduce PRCL too. If not
4. investigate the interesting fact that PRCL and REFL_RIN seem to show the same coherence with DARM