A couple of sensors currently have increased 60 Hz noise. It’s “ok” to run as is and just mark them as bad channels if the usual notch filter (or other power line cleaning approach) is not enough to clean this.
The affected channels right now are: MRO12 and MLO11.
This is very likely due to condensation in the pre-amplifier cavities on top of the MEG. Usually this happens right after the MEG is cooled down during a long service (once a year), but here it seems due to an accumulation of frost at the top of the MEG that lasted a few days, related to helium refills. It can take a few days to dry up and the artefact to go away.