If there's a small brown bird trying to build a nest in a dumb place, it's probably a Carolina Wren. 

I joke, but there was at least one spring growing up where my parents couldn't use the range hood on their stove because Carolina Wrens built a nest in the exhaust vent. 

At another house, I thought neighborhood kids were trying to mess with us by stuffing our wall-mounted mailbox full of sticks every single day--until I realized that all of the sticks were tiny, uniformly matchstick-sized and there was a small brown bird that seemed to be yelling at us every time we came out of our front door. We bought a small birdhouse, hung it in a tree twenty feet away, and everyone was much happier. 

They're very fun and active birds to watch. You usually hear them before you see them. And when a nest is built in an appropriate place, it's exciting to watch the doting parents and peek in on the babies.