I injected noise on lenght d.o.f of the end mirror when FC is locked and measured its TF to legth oplev and correction signal to the laser piezo.

The TFs look similar (pic 1) even if they are not very clear and the coherence is quite low. (pic 2).

The noise amplitude was 10000 count (~3V) and the driving matrix was such that only vertical coils where used. (It should couple only with pitch)

Pic 3 shows the spectra of the other d.o.fs. The damping loops were closed at that time, but pitch shows a motion larger that usual.