I'll run the first question: Why do I many times feel like a lump in my throat toward the end of chazzaras hashatz (when I'm the baal tefillah, of course)? I tried lowering my voice (volume), but that helped only a little.
The 'lump-in-your-throat' feeling comes from tension. For example, when you swallow, your neck starts to tighten up. Try that now... Put your hands on your neck and swallow... It's something that happens when we're nervous, tense, anxious (not necessarily from being up on the amid but could be from daily matters like family, money, job, etc.
It could be from not using your vocals properly - example, when your larynx (that's the Adam's Apple area) are high, then people tend to sing from their throat. As opposed to singing (rather, supporting) from their diaphragm (in the stomach.)
When you say you tried lowering your voice - what did you mean? Volume; as you put in parenthesis, like one would do on a boombox, to lower the music, or lower meaning, you brought down the key? Just to clarify.