This is a mud-dauber wasp nest
Info taken from the UGA publication Stinging and Biting Pests
Pipe organ mud daubers are elongated, slender and usually shiny-black wasps that vary in length from about a half inch to an inch or more. These wasps make their mud nests with the cells arranged in the form of long tubes, hence the common “pipe organ” name.
Individual wasps make a buzzing sound as they shape mud into a nest and provision it with spiders for their larvae to feed upon during development. The female wasp stings and paralyzes the spider and then lays an egg on it and seals it in the mud tube. The nests are often in protected but open areas under the roof eaves of buildings or sheds. Mud daubers rarely sting and are generally considered beneficial in reducing spider populations.
Learn about many more of these type pests in the UGA publication Stinging and Biting Pests