This looks like the nest-building activity of a cicada killer wasp or another type of solitary wasp. The cicada killer wasps are active now (they hunt cicadas to feed their young). The males cannot sting, and the females will not sting unless they feel threatened. Since they are valuable pollinators, we discourage using any insecticide on them and encourage tolerance during their period of activity. These two links provide further information about them and what you can do. 

Cicada Killer Wasps
Cicada Killer Wasps are Scary But Good

Christa