Bump in the night

So around 3am last night (this morning) my dogs started barking and woke me up ... they ran to the front door and barked and barked and barked - so I went to the front door very frightened - looked out the little window and saw nothing. They ran back into the bedroom (the windows of my bedroom are on the front of the house, right by the front door) and barked and barked - so I went back into my bedroom - where the curtains were open (yeah, I hardly ever close them) and didn't see anything. Then I hear something knock on one of the windows - but I still see nothing. So I take the dogs back to the front door, turn on the porch light, open the door and let them out - thinking if there's something (someone) out there, they will get 'em. They just stand on the porch and bark - so I very timidly walk out and look in the bushes by my bedroom window and see no one. Then I go back on the porch to go back inside and hear 6 rapid "bangs" like fireworks or gunshots. I jump in the house, look back out the window and still see nothing. The dogs calm down a few minutes later, needless to say I got very little sleep after that. I still have no idea what went on, or if I was just so freaked out by them barking that I was imagining sounds or what!