Hi
Bridget! The Walt Disney World Resort is a magical place for many people, including people with Asperger's Syndrome and their families.
I will recommend obtaining a Guest Assistance Card (GAC) from Guest Relations at any Disney theme park once you arrive on property. A GAC is for guests with a wide variety of special needs, including "invisible conditions." Each GAC will accommodate the bearer, and up to five other members of the travel party, by allowing access to alternate attraction entrances where available. A GAC will not necessarily give your family front of the line privileges, but typically you'll be accessing attractions through more secluded areas.
Once you arrive at Guest Relations, please explain that your son has special needs. Be ready to describe his specific challenges. The Guest Relations Cast Member will add a stamp to the GAC alerting attraction Cast Members as to the type of special assistance and accommodations he may require. Please be advised that in order to use the GAC, your son must be present when entering attractions. You won't be asked to provide proof of diagnosis, so you won't need a doctor's letter in order to request a GAC. However, it is always wise to bring medical documentation to have handy in case of any unforseen emergencies.
Since your son is sensitive to loud noises I will recommend bringing ear plugs for evening fireworks. Some shows and attractions can be quite loud too. Therefore, I suggest sitting by the exit areas and/or asking Cast Members about the attraction's noise level before going in.
Please let me know if I can be of any further assistance. I'll be glad to answer any questions you have regarding this matter. This is the year of making memories at the Walt Disney World Resort. May your family enjoy making many lasting memories together!