Unusual underground noise

I was trying to post this in the Geology Forum but not sure if that is what happened.
I have a piece of property in the berkshires in western mass. There is an unusual noise that I occasionally hear and it has me mystified. At first I assumed it was someone trying to start a a large tractor or machine off in the distance. It sounded like a put...put...put.put.put.put. With the "put's" getting closer and closer together. the whole sequence lasted 3-4 seconds. I would then hear it repeat after 3-5 minutes.
After a few months I began to wonder what this machine was that wouln't start. since the area is very isolated and primarily state forest I also wondered where it was. It sounded like it was maybe 1/4 - 1/2 mile away.
This is when it got strange. When I drove toward the noise along my property line and stopped to listen I realized the noise was behind me! It was on my propety (60 acres). When I would walk through the woods to locate it it would seem to move about. I could never get there. It felt like I was chasing a rainbow.

Any ideas?