The leak underground was a solution to the air noise; but not an economical one. The leak permitted air to leave the pipe. During the leak repair, the water was turned off and the pipe drained. After the repair, it is likely that some air was trapped in that section to make noise; it probably will be absorbed in the water over some time and the noise may disappear. It would be very expensive to excavate again to install a little air relief pipe. Perhaps time will solve the problem.