As you might guess, I could not come up with a succinct, short question, so here is the background story to the question.
A while back we had a leak in our water line from the meter to the house. It was not surfacing so we borrowed a listening device from our water department to see if we could hear the water "hissing" as it left the leak.
The listening device is basically a sensitive microphone that is encased in a cup that you put to the ground and a headset to listen. While searching, our daughter wanted to give it a try so she went around the yard a little bit listening, not following the water line, just random.
She suddenly started laughing and when I asked she said it was because she was listening to both sides of a conversation in FRENCH. Of course I wanted to hear and sure 'nuf, both sides of a French conversation. The conversation eventually drifted away and we do not know what was being said because we only knew enough French to know it was French, but how could we have picked it up?
My mother-in-law has long said she hears a radio station in bed at night and she is almost totally deaf without her hearing aids. She takes them off when sleeping so it is not the hearing aids.
Sometimes it is music and sometimes voices but she has never been able to tell if it was English or something else. She does not have a radio in there and coincidentally, Melissa heard the voices about 40 feet from her bedroom.
Now a little topographic information about where we live. We are near Bell Buckle, live on a hill that has caves underneath and water runs through the caves. We don't know the amount or depth of water since it was determined by some spelunkers from an MTSU cave club who dropped rocks into a "room" they found about 60' deep. They were about 30' deep and measured the time a rock took to hit water.
They would have had to excavate to go lower and we did not feel comfortable with that. They did not hear music or voices and were about 60-75 yards from the house.
So, back to the question. How could sound waves travel from somewhere (maybe a few miles or many) and get picked up by a ground microphone.
My mother-in-law could be a separate issue, but she hears music and talking in other specific places in Bedford County that we pass frequently so I believe she is hearing it. At these times she does have her hearing aids in so it could be intercepting radio transmissions or even cell phone calls I suppose, but it is always at the same places. (Don’t worry folks, she can never hear well enough to know what is being said)