The volume on prayer

I listened to WMBI around 1pm for Pastor James' show (the head pastor at Harvest Bible Chapel in Rolling Meadows) and he said something that makes sense to me. He said that when you pray, you should pray aloud because if you sit and pray silently, your mind starts to wander. Then, you're distracted and you may not even be praying truthfully anymore. He challenged people to try that, to pray out loud... you are more focused when you do. He has a good point, and I wonder about all my Christian friends who end up praying aloud. Did they already know this about praying and focus, or do they just pray out loud coz that's what they were taught? And what does that say about praying Catholics? I don't know a single Catholic who seems comfortable praying out loud (except the priest). They all bow their heads silently. Why is that?