Let me clarify: the hum comes from the other pedals, even when all audio cables are unplugged from the H9 so that the H9 is not in the signal chain. The only connection of the H9 to the rest of the system is through the daisy chained power cable, so it’s reasonable that the problem does not occur when that cable is removed and replaced with a separate power supply cable. Because the only ground connection is through a single cable I don’t think it can be a ground loop.