Why does the church bell ring at 12 noon?

To commemorate the salvation of Christian Europe from Muslim invaders. Specifically to honor Hungary (also know as Magyars), which sacrificed so many of its people to protect the rest of Europe.

"…Hungary was also Christianity's bulwark against the invasion of the Tartars and Turks.1" "…which are expressed in some everyday practices such as the pealing of bells at midday…2"
1.MESSAGE OF JOHN PAUL II TO THE HUNGARIAN NATION FOR THE MILLENNIUM OF ST. STEPHEN CORONATION From Castel Gandolfo, 16 August 2000 - Archives of the Vatican
2. ADDRESS OF THE HOLY FATHER JOHN PAUL II TO THE NATIONAL HUNGARIAN PILGRIMAGE Monday, 9 October 2000 - Archives of the Vatican