Hi, Serena. Wow, this is quite a challenge you've got here. How does your son relate to your older kids? Is it just little ones' voices he can't stand?
I only have one suggestion that hasn't already been brought up, and it may sound too simplistic, but it's worth a shot. Have you tried ignoring your son's behavior? I know he's only a year old, and it certainly would alarm me if my child were working himself up to the point of throwing up, but maybe that's how his body reacts to that kind of emotional turmoil. It might help him to see that Mommy doesn't think there's anything to get emotional over. My six-year-old has always been emotionally "sensitive" as well. I know much of the time, my son's behavior depends on how I present the certain situation to him, and if he sees me tiptoeing around him, he takes that as a sign that there's something to react to. If I act like it's not a big deal, he relaxes.
Your dedication to your son's well-being is wonderful, Serena, but if you try to drown out all the noise, or whatever else upsets him, you may only end up making him more sensitive. Just my two cents. :) I wish you and your little guy the best!
(Hey, by the way, congrats on 10 years of marriage. My husband and I will celebrate our 7th anniversary, God willing, in April, and it's been a fulfilling but tough road. Especially nowadays, I admire those who make it to the decade mark!)