The input sensor signal of the top mass of the beamsplitter have been moving suspiciously for two days.

Attached is a spectra showing a comparison of F1 top mass sensor on July 09th 2013 at 13:00 PT (pink) and same day at 14:00 PT (blue). The blue curve is higher at around 60Hz which might be why we see the anomalous signal on the osems. The second level of the suspension , and stage 2 of the ISI are not moving at this frequency (cf second pdf).