Very low deep rumbling noise from the sky,but no airplanes in sight.On July 21, 2016, I stepped onto my patio around 9pm. It was dark with broken clouds overhead. I heard a very deep, rumbling noise from the sky. We do have the USN Blue Angels flying team nearby, so I eagerly looked for their appearance, but to no avail. The noise sounded as if there was 15 of those jets, but high enough in altitude it did not hurt my ears, but loud enough that I expected to see them for sure. After 30 seconds or so, with the noise continuing, I called my husband out to the patio. It took him about 30 more seconds to come to the patio and I told him listen...that noise has now been going on about a minute. It seemed to continue about another minute. The next night while listening to Coast to Coast, I heard Peter Davenport speak of a man from Daphne, AL, who heard exactly what my husband and I heard on the same evening. I'm, in Mobile, AL. And daphne is not far from here. Just a note this noise was heard 7 miles from Mobile airport.. I heard n! o other planes taking off or landing during this time.