Thunderous blast

First of all, keep in mind this town is rather small. Most of the towns residents live on Mainstreet which is less than a mile long and is a part of the Old National Road. The town only has four roads running east and west, but there are many alleys and side streets. In short the village is pretty  much clustered in a small area. Last Saturday night as I was working in my garden, just as the final rays of light were passing into the evening shadows, I heard the first of several volunteer firemen come down the street and hurry into the fire station. Within less than a minute the firetruck, siren blazing, had headed out of the station and west on mainstreet toward the Interstate. The firetruck had had about enough time to leave the village limits when a thunderous blast was heard that was so loud the ground shook where I stood. I wondered if the Firetruck had hit something. My wife came out the backdoor of our house which faces our garage and garden, asking what on earth happened.  I assured her I did not know. Strangely, I did not see another neighbor anywhere. The blast was loud enough to (my wife said) rattle the windows in our house; surely others were curious....wouldn't you think? My wife got into our car and drove around town looking for the source of the explosion. She came back, shaking her head. "I saw absolutely no one" she said. "Nobody in their yard or along the street to ask, nobody." This is strange, the town is small, but usually busy on a week end. Today, I asked around at church and the neighbors.....strangest thing.....none of them heard a thing. You tell me.