Been there before. Try two things: 1) sound muffling headphones. They will reduce ambient noise but he'll still be able to hear what you're saying to him. This helps with sensitive to noise. 2) whisper when you talk to him or talk very softly if he has the headphones on. This will make him stop what he's doing so he can concentrate on what you are saying and he may very well start talking softer to mimic you or match your tone without even realizing that he's doing it. Also, airplane, storms, and crowds can be overwhelming and you could try teaching him some relaxation and self-soothing techniques (which is still going to be hard).

my son is very loud and i just remind him "inside voice" and he lowers it. Sometimes i have to remind him several times because his volume will gradually increase but now i don't even wait for a break in the conversation, i just say it while he's talking and he does it without even thinking or stopping his flow of speech. I say it softly and sometimes make a hand motion if we're with a group of people and they usually don't even notice i've done anything to correct him so he's not embarrassed by it.

Sensory Integration Dysfunction. Noises REALLY bothered my guy until he got older.

Check out Facebook autism discussion page. It will answer your questions and then some.

Been there before. Try two things: 1) sound muffling headphones. They will reduce ambient noise but he'll still be able to hear what you're saying to him. This helps with sensitive to noise. 2) whisper when you talk to him or talk very softly if he has the headphones on. This will make him stop what he's doing so he can concentrate on what you are saying and he may very well start talking softer to mimic you or match your tone without even realizing that he's doing it. Also, airplane, storms, and crowds can be overwhelming and you could try teaching him some relaxation and self-soothing techniques (which is still going to be hard).