I'm just west of Bloomington, IN, 4-5 miles from the Monroe County-Green County line. I just heard a large number of thunder-like booms, and they weren't coming from the sky. There's also a gradual rumble that seems to be lasting for 10+ minutes on end before taking a quick break, then starting up again. Where I'm at, there's karst topography, with sinkholes and cave networks everywhere, and this entire area of Indiana is situated on massive quartz deposits. My dogs are laying down and they look kind of scared. There's a whole flock of birds that came and went about 20 minutes ago, and they were acting very strange for the birds around here.