Upon arrival inspected system and found no major concerns. Listened for noise once in attic and couldn’t recreate noise they were getting. It is only when the furnace is running it was rattling was the information I was given, couldn’t get any noises from unit. Moved a large rodent trap to get to furnace, suspect the rodent trap was rattling because it engaged as soon as I bumped it. Informed homeowner to call us back if noise continues but cannot recreate noise at this time.