Hopefully it is just a quick visit because those things smell really bad when they congregate and produce LOTS of poo also. They love high points so the breeze will waft in the glorious smell of rotting carrion. They like perches and roosting areas that don't restrict their huge wingspan when they launch like water towers, cell towers, dead trees with few branches......and nice rails on decks that have a great view.
At night when they roost they'll fuss and squawk with each other and flap their wings loudly. If their visits start to become a regular thing I highly recommend discouraging them early on, humanely of course....they've got a valuable service to perform, as you know.