It is, or should be a well known Halacha that when davening Shemona Esrei one should say the words so they can hear themselves but no one else should hear them. Meaning you should not say your Shemona Esrei so it is audible to others. One can see this halacha written in almost every single siddur whether in the back (artscroll) or before Shemona Esrei in many all Hebrew siddurim.
If this is a Halacha, how come many people don't follow it. When I am trying to recite Shemona Esrei, I do not need to hear someone else's. There was an article on someone's blog which I don't remember about whether or not you should say Amen to someone's Bracha during their Shemona Esrei if they are saying it loud enough for you to hear. My first reaction after reading this was that you shouldn't be able to hear someone else's Shemona Esrei so this shouldn't be a question. Apparently that's not the case. People tell me that when you go to shul that you should just sit away from these people. What if they come late and plop right next to you? What are you supposed to do? In the neighborhood I live in, I can identify who some of these people are so I can sit on the opposite side of the shul of them. What if you can hear them even if you are on the other side of the room? What if one of these people is a Rabbi in the community? You would think that a Rabbi would know this halacha. If a person has a hearing problem so they can't hear themselves which is why they are loud, don't they realize? Why can't they go in a corner and daven in a way so the sound doesn't travel and disturb other people? Do some people daven out loud because they want everyone to hear that they are actually davening?? Which is worse, talking during the rest of davening and disturbing people or saying Shemona Esrei out loud and disturbing people? It is a halacha as well ,ven though people do it, not to shout out Yaaleh Viyavo in the middle of Shemona Esrei to remind people to say it. I always find that the people who do this usually rush through their Shemona Esrei so they can be the first to scream Yaaleh Viyavo like they are the entire minyans savior for saying it. Rabbaim developed ways to make up for skipping it by accident, because people are not supposed to shout out Yaaleh Viyavo. I thought the universal custom amongst all Jews was to bang twice on the shtender to remind everyone Before they start their Shemona Esrei. By bringing up these issues, I don't feel that I am being critical, these are just things that drive me nuts. Maybe the Rav's of shuls should make little halacha reminders before davening so these things shouldn't happen. The only problem with this is too many Jews don't listen to what Rabbaim say anyway so it wouldn't make any difference.