When we shook every chamber with external shakers, the BS chamber produced the most upconversion. The peaks produced by line injections have large side bands, suggestive of scattering (https://alog.ligo-wa.caltech.edu/aLOG/index.php?callRep=25132). Figure 1 shows photographs of things that might move in the light when the BS isolation shakes. These are pictures from the point of view of the beam spot on an ITM compensation plate or a beam spot on the BS itself. The ITM eliptical baffle is an obvious candidate. The baffle is mounted on stage 0 of the BS isolation. To test that it might be scattering, I shook stage 0 and stage 1 on Monday at two slightly different frequencies. The results in Figure 2 are consistent with scattering from something on stage 0, but not stage 1 or 2. I think we should B&K test the ITM elliptical baffles at LLO to get resonances for further testing of the hypothesis that we are seeing scattering from the ITM elliptical baffles.