Hi Sarah -
Thanks for posting your question. Many of our children show sensitivities to sound - and there are many things you can do to help him.
First, I would suggest making sure that William has some time each day when he is in a distraction-free controllable environment - e.g. his playroom, his quiet bedroom, another quiet room in the house, etc. If you've watched our Inspiring Stories DVD, you will have seen Jordan, a little boy from the UK, who had extreme sound sensitivities when he arrived here for The Son-Rise Program Intensive. By the end of two weeks here in our distraction-free, controllable, quiet playrooms, his parents suddenly realized that he was no longer screaming when the lawn mower was going outside their apartment. A distraction-free and controllable environment can really help our children dramatically - because it gives them to let their brains process sound input, so their brain can learn to manage different sounds more easily.
In the playroom, you can experiment with different sounds. When William is in control, perhaps he'd let you talk a little louder today, if you slowly and gently work up to the higher volume. If he says stop, you immediately stop. But you can play with slowly and gently introducing new instruments, new sounds, new volumes, etc. - with William being able to say stop whenever he wants to.
Also, when children are going through a particularly sensitive phase, we suggest to families to do the crazy and unthinkable - to vacuum the house ONLY when necessary - or as little as possible. I often find that some moms clean the house frequently simply because they like to have the house really clean. But your house can survive without being vacuumed as frequently - so if you vacuum less, then you're again giving William time to feel more relaxed, so his brain has time to learn to process sound more easily.
Finally, I would also suggest looking into the different forms of auditory integration training (AIT) that are available - there are a few different types of AIT - all helping William's ears adjust to a variety of sounds. You can research AIT or look into the Listening Program, another form of sound integration therapy that you can do at home in the comfort of your own playroom.
Let us know how it all goes - we'd love to give you more suggestions if you want them.
Son-Rise Program Teacher
The Autism Treatment Center of America