There is a weird "earth" sound that I hear, most often in the spring and wondered if anyone knew what this could be. It seems to come from the small mountain/large hill across the road from me. Almost sounds like an old diesel tractor starting up, running for 5-6 seconds or so then stalling....kind of a putt, putt, putt, put-put-put-put, putt, putt sound. There's nothing but woods for several miles in that direction so I really doubt it's anything man-made. As I mentioned, it seems to happen most in the spring, is often heard right after a vehicle has driven by though it does it at random other times too. I'm guessing it's caused by the ground warming up, but was curious if anyone else has ever noticed this.