As per Discord discussion:
20 Hz noise from the power over coax design in this headstage is a known issue on 1 channel of headstage-64 when the electrodes are floating.
Appears on all channels when probe not in the brain. When you actually use the headstage in the brain the issue is resolved on all channels except for 1 that is closest to the power supply.
Leaving half the channels floating will not help the situation.