I have been hearing a loud rumbling noise for several years now at my home. I live in Nichols Hills east of Penn. and south of Britton. The sound emanates from southeast of my home and appears to be coming from 5 to 10 miles away from somewhere on the ground. It is completely random in occurrence. I hear it at various times of the day and night. Sometimes it will only happen once and other times it will do it 3 or 4 times in a row over a 20 minute period. It always begins low in volume then builds to a loud rumble then fades. It sometimes lasts only 10 seconds and others times goes for up to 3 minutes. I can hear it easily when I'm inside my home and If I'm outside I can actually feel it in my chest and have to raise my voice a little to talk over it. I have called every agency I can think of and no one has heard it themselves or had it mentioned to them. My family and friends have all witnessed this sound. It does not move around. It always comes from the same place. Any idea what this is?