This time his task is not an FBI case; it's the friend of his father-in-law. Naturally, he has to be more meticulous and eliminate all possibilities.
The previous private detective's mention does carry some weight, as low-intensity seismic waves can indeed cause certain buildings to resonate. However, this is uncommon, and this phenomenon has only occurred in the last two weeks, which isn't very likely but is still one possibility.
The second possibility is animals, like in a novel he once read, "Rats in the Walls," where a group of rats gnaw at the materials of the building or make squeaking sounds, creating a similar effect, especially if it's happening all around, forming a surround sound.
However, this is right next to New York State's second-largest city, Buffalo. It's unlikely that such a place would have a villa infested with a large number of rats. If there were that many rats, Harlington and his team would have discovered them long ago.
