Why are there explosions everywhere?

Sometimes when I'm playing Bastion there are small explosions on the map. Not necessarily near me, or near any enemy. What's happening? Am I being shelled?


If you have the Acobi idol turned on then enemies will drop live grenades when you kill them. The grenades weren't very easy for me to see all the time so it looked like random explosions.

http://bastion.wikia.com/wiki/Acobi