Modesty in davening?

Judaism is supposed to be a religion that prides itself on modesty and humility (yes, that statement is intentionally ironic). Obviously, we place a great deal of emphasis on manner of dress, but we understand that our general comportment should be one of not calling attention to ourselves unnecessarily.
That's yet another reason I don't understand the whole "G-d is deaf" crowd. And why I don't understand why so many people insist on calling attention to themselves - in (what I would consider) a negative way. I know of several people - varying degrees of "religiosity" and backgrounds - who insist on screaming the first pasuk of Shema (yes, I know there's a halachik basis for saying it out loud. Surely there's also one for not interfering with other daveners' kavanah). A very high percentage of those same people are saying it wrong! Some, for example, finish the last word - "echadduuuhhhh." Others - "echa (pause) aaad".
Do I do it perfectly? I'm sure I do not, though I do it as best I can. Part of my point, though, is that at least not everyone else knows how wrong I am when I say it! And I'm not bothering anyone else when I do it (unless someone gets upset by others saying Shema relatively silently. I suppose that's possible).