This is mostly to record something weird I saw after switching blends. I don't think the performance of the interferometer is affected. Take if for what you will.

I installed new isolation filters on ETMY today, and while watching the ISI to make sure the loops were stable I found something weird. At first I was worried that the ST1 Y loop was broken because the ISO output spectra was higher than X by an order of magnitude over ~40-150 hz, but then I realized the blends were different (X was using 45mhz, Y was using 90mhz). I switched the Y blend to 45mhz and the output dropped to the same level as X. When I switched Y back to 90mhz, after the blend switch completed ~20 seconds later a very unnatural "shelf" appeared in the output spectra ~200hz (mostly Y, but others too). This shelf raised the noise as it moved down, and stayed high after the shelf stopped visibly moving. I'm not clever enough to put a video together, but the 3 attached spectra show the story. The first is the shelf forming at ~200 hz, the second is the shelf moving down in frequency, the third is roughly when the shelf stopped moving. I watched the time series of the local sensors, supersensor and ISO out while this was happening but I saw nothing obvious.