The Imaam of our Musjid makes a long loud Dua after the Fardh of Jumuah.

Answer

This method is bid'ah. After the Jumuah Fardh, as well as after the Zuhr, Maghrib and Isha' Fardh, there should be a short silent Dua such as Allaahumma antas salaam… Immediately after this short dua, engage in performing the Sunnat Salaat. After completing the Sunnat and Nafl Salaat engage in Tasbeeh and long silent dua individually, not congregationally. After the Fardh of Fajr and Asr, engage in Tasbeeh and long dua as much as you wish. The Dua should be silent. The loud Dua and saying 'Aaameen, Aaameen' are bid'ah. Furthermore, it is not necessary to begin and end the Dua with the Imaam. Everyone is free to do as he pleases in this regard.