This 2 Hz comb is actually glitches every half a second. It seems like the period is not exactly half a second. They appear in DARM but not MICH, SRCL, or PRCL, so it's probably not a bad PR or SR mirror driver. Attached are a few Omega scans. The first is several seconds long and shows that these are very short and span about 40 to 100 Hz. The next three Omega scans are 4 seconds apart, showing that these don't sit right on the integer second and have a period that is not quite 0.5 seconds.
The comb shows up in the ETMY top stage F1, F2, and SD but none of the others. See attached plots.
Nutsinee, Thomas A., Ran omega scan for 1126336348 (Sep 15 2015 07:12:11 UTC), and found that the once-per-0.5s glitches repeating glitches are noticeable in: H1:OMC-DCPD_SUM_OUT_DQ H1:ISI-ETMY_ST2_BLND_RZ_GS13_CUR_IN1_DQ H1:ISI-ETMY_ST2_BLND_Z_GS13_CUR_IN1_DQ H1:PEM-EY_MAG_EBAY_SUSRACK_QUAD_SUM_DQ H1:PEM-EY_MAG_EBAY_SUSRACK_X_DQ H1:PEM-EY_MAG_EBAY_SUSRACK_Y_DQ H1:PEM-EY_MAG_EBAY_SUSRACK_Z_DQ Full omega scan: https://ldas-jobs.ligo-wa.caltech.edu/~tabbott/H12HzComb/