There is no 'divine reason' for praying aloud. Because God can hear our prayers in secret (Mt. 6:6-7) and even in silence (Luke. 6: 12, Mk. 1 :35). But we have personal and social reasons for the same. We have personal reasons to praise aloud. Man is a rational being as well as emotional beings. Our emotional love finds an outburst in loud prayers. Moreover many of our tensions are released when we praise aloud and sing aloud. Good and pious songs have therapeutic effect on our troubled mind. We are asked to love God w h all our heart, with all our soul, with all our mind and with all our strength (Mk.12: 30). We have to love God with all our physical, psychical, emotional, and spiritual powers sound is also a gift of God - a God-given power which we have to use for His praise. "Whoever confesses me before men, him I will also confess before my Father who is in Heaven" (Mt. 10:32: Luke. 12:8), says Jesus. We have also social reasons to praise aloud. Man is a social being and needs social gatherings. When people are gathered in Jesus' name, there his presence is experienced in a deeper level. When thousands pray in one voice, that becomes an exhilarating experience and even the luke-warm hearts are burnt with God's love. A silent prayer by thousands gathered, may not be (so intensive) Community praise and worship will liberate us from many fetters such as addictions to liquor, smoke etc. According to Acts 16:25-26, even physical liberation, of Paul and Silas, was made possible through loud praise and worship. During his public life, Jesus didn't discourage those who shouted his praise. Though the disciples tried to silence blind Barthemaeus who shouted, Jesus, son of God have mercy on me" (Mk 10:46-52), Jesus heeded his prayer and cured him (Luke 18:35-43). When Pharisees asked Jesus to rebuke his disciples for singing praise (Halleluiah) to him, Jesus' answer was, "I tell you that if these should keep silent, the stones will immediately cry out" (Luke 19:39-40).
The faith in Jesus is to be lived as well as to be confessed. "If you confess with your mouth the Lord Jesus, and believe in your heart that God has raised him from the dead, you will be saved" (Rom. 10:9). 'Jesus who was crucified was risen by God' was the content of early Christian preaching (Acts 2:22-24). The Apostles witnessed Christ (Acts 1 :8) not only in their life but also in their preaching (Acts 2: 14 . That is why they were commanded by the civil authorities, not to preach (Acts 4:5 . "But Peter and John answered and said to them, "whether it is right in the sight of God to listen to you more than God, you judge. For we cannot but speak the things which we have seen and heard" (VV 19-20). The spirit came on the Day of Pentecost with a sound from heaven as of a rushing mighty wind (Acts 2:2). Hence when a group of those who have received the spirit come together for praise and worship, one must tolerate some noise. These centers encourage large congregation, only because they want to benefit maximum people with minimum resources.
One must notice that only during the time of common praise and worship, so much noise is produced in these retreat centers. At other times silence prevails. During the time of breaking the word all listen carefully and assimilate the word to their life. For they are aware that "God is not the author of confusion, but of peace" (1 Cor. 14:33).
Many of those who come to these retreat centers are broken people. It is natural that they shout out of joy when they experience Jesus as their savior, as their liberator who frees them from all the fetters of sin and addiction. It is recorded in Acts 3:8, that as soon as Peter cured the lame man, "leaping up ha stood and walked and entered the temple with them - walking, leaping and praising God". "And all the people saw him walking and praising God" (V. 9).ln the Divine Presence, one cannot but express his joy. What did David do in front of the Ark of the Lord, "Then David danced before the Lord with all his might ... so David and all the house of Israel brought the ark of the Lord with shouting and with the sound of the trumpet" (Sam 6:14-15). When Mary, hearing the son of God in her womb, visited Elizabeth, the babe in Elizabeth's womb leaped in her womb and she received Holy Spirit (Luke 1: 41), so one can understand the shout of joy and jubilation of those broken-hearted people who meet the Lord face to face in these retreat centers and who experience "how sweet is the Lord". So let us "sing aloud to God our strength, make a joyful shout to the God of Jacob" (Ps 81:1).
Some comment that 'praise and worship' and 'conventions' are not "Catholic". But this is not true. As Catholic Church is the continuation and extension of he early church, the heritage of the early Christians belongs solely to this Church. In the early church, people gathered together for prayer and worship, for hearing the word of God, for common meal, and for breaking the bread and had even a community life sharing all material goods (Acts 2:42-47). In the course of history some of these aspects became dormant in the church, whereas some denominations which were separated from her from time to time revived some of these aspects. Let us laud them for reviving and keeping some of these aspects, and at the same time be proud of returning to our past. "Let all those rejoice who put their trust in you; let them ever shout for joy, because you defend them; let all who love your name be joyful in you" (Ps 5:11).