I don't think its my ears and my wife hears it too. I guess it's at about 70 Hz? It's very constant in frequency and maybe I'm only hearing a harmonic of a lower one? Took a little drive about a mile out and its still there, a good distance from any industrial buildings. Drives me a little nuts. My laptop and phone mikes don't seem to pick it up, I don't see any discernable peaks in the spectrum analyzer with Audacity. Maybe there is a pump running somewhere, since we had torrential rainfalls since about yesterday. But to still hear it, almost two kilometers out?!?