I took JeffK's recent B&K data for SR2 and plotted it against Arnaud's data from 2014 (alog 12089). Jeff's measurement is very different from what Arnaud found. There is a new resonance at 50 hz in both degrees of freedom that is sharper than any of the resonances from the 2014 measurement. Talking to Jeff and looking at Arnaud's setup, it looks like the sensors were in different spots, but the strike locations were the same.  It also seems that my tfs on HAM4 on Nov 8th show this some, second attached image is the gs13 cartesian tfs from that measurement. The 50hz feature shows up most in the rotational dofs, but is pretty small. I don't think it's hepi, because the other chambers don't see a similar feature.  Not sure if this will be an issue for the ISI controls yet, but probably not. Jeff also suggested SR2 was locked for this measurement, so I'll try a shorter set of tfs tonight before I leave, if the LVEA gets quiet.