I used Evan's script to step the 9 MHz modulation depth down by 6 dB.  This was inspired by Koji's alog pointing out that the 9th order 9MHz HOM lines up pretty well with the carrier TEM00 mode (alog 29399), and so is probably what we're seeing on the camera view of OMC Trans.

This noticeably improves the image at OMC Trans - see attached screenshot of camera views.  Both have an exposure of 35000.  Left is nominal, right is -6dB for the 9MHz. 

It also reduced the DARM noise between 900Hz-1kHz.  In the attached spectra, dark purple is the nominal 9 MHz modulation depth of 16.8 dBm, and bright red is the lower modulation depth of 10.8 dBm.  There's perhaps a bit more frequency noise at several kHz, indicating that the CARM gain isn't being increased quite enough (it was increased for this screenshot by 7dB from a slider value of -5 to +2 on the common mode board's IN1 slider).

Tomorrow I'll add this to the ReduceModulationDepth guardian state.