midnight
`` The presence of a man or woman in that room would be evident to a person listening miles away , '' he went on . `` A high-frequency current is constantly passing through that storeroom . That is what causes that normal buzzing . '' It was verging on midnight when Kennedy suddenly cried : `` Here , Walter , take this receiver . You remember how the buzzing sounded . Listen . Tell me if you , too , can detect the change . ''