End of the critter story
Well, the first post by Talkjk was very, very close to the the cause.
What I was sure was a critter, came back... in spades... Loud, Loud bumping in every room in the house.
At wit's end, I decided to call public works, in my City of Peru. One of the nice things about living in a small town, is that people are great. Yesterday two nice guys came out to the house, and spent 3/4 of an hour, tracking down the cause. Not easy. Into the crawl space, and then checking out every possible source for the problem. Fortunately the problem was at it's peak so they could hear the bumping..
The problem was not in the house, but under the front driveway to the house. Between the driveway water shut off to the house, and the street water main, there was a leak in the brass fitting.
Going back a bit, when we moved in, in 2004 our driveway of 12' x12' concrete slabs, has one that had dropped down about 1/4 inch. Gradually, over the years, this grew to 1/2 inch, no big deal, but obvious. Turns out that the leak in the pipe, under the driveway had caused the soil to wash away and the slab to drop. It was on the city's side of the valve.
Anyway, the problem is solved. Slow water leak outside the house. It means that I get a new driveway and the noise will be gone. Total cost to me $00.00 instead of the $2000. estimate I had received to repave the slab. I love the town where we live.
Whew!
Here's the first post that came close to the problem.
Are you sure its alive? Could it be water hammer in the pipes? Your pressure regulator could be failing and as a result the pressure in a line could cause water hammer in the pipes. A leaking toilet could trigger it each time it fills and shuts off.