Weigang Liu tried folding DARM and selected magnetometer channels during the three days of ER9 (UTC days)
with results posted here:  https://ldas-jobs.ligo.caltech.edu/~weigang.liu/advancedLIGO_3/ER9/files/ER9_magnetometers_and_strain_list.html,
where DARM folding focused on the 10-50 Hz band, and the magnetometer folding was low-pass
below 50 Hz, choices motivated by O1 experience.

As expected, the magnetometer channels still exhibit a variety of pathologies with 2-second periodicity,
but the elevated low-frequency noise in DARM make it hard to see this 2-second contamination in that channel
with this method. Attached are a few sample magnetometer fold summaries over the three days.