The 42 Hz peak looks to be part of a comb of 1 Hz spaced lines which is well visible in CEB UPS current voltage monitors. The noise has disappeared now. From past investigations (https://logbook.virgo-gw.eu/virgo/?r=40113) a possible source of this comb are the TCS laser chillers. In a study performed at that time with the TCS team we found that when setting the chiller in "power save" mode the comb disappeared.

The second figure shows that the comb diasppeared yesterday morning (maintenance time). It has to be better checked if some operation with the TCS chillers occurred at that time