The house was quiet, kids in bed, I was talking with my wife in our bedroom when we heard a VERY LOUD "BANG!" It sounded like something severely hit a wall in our basement. 30 seconds later we heard the same thing. It really freaked us out. I grabbed the shotgun, but before I proceeded downstairs to check it out we heard a 3rd (and final) "BANG." We searched the house, nobody or nothing in sight. I went outside to check the home exterior and property, saw my neighbor and he said he thought he heard a gun shot. I checked the furnance and noticed it was really dusty so I cleaned it and went to bed. I researched online about "loud bangs in home" and discovered it may be a delayed ignition (but 3 times?), or it may have been excessive water pressure or air in the plumbing. Furnace and plumbing technicians who arrived the next day said everything looks perfect. What's going on?