If his social skills are in order, he is probably just a bit sensory defensive rather than autistic. Get your hands on the books on sensory integration (Carol Stock Kranowitz "out of sync child" or Sharon Heller "too loud too bright too fast too tight"). There are some things you can do at home to help, but inform yourself first.
My kiddo nearly 5 years old is high functioning autistic and also sensory defensive, getting easily distracted, sensitive to food texture, does not like to get his hands messy, will cover his ears sometimes (not too often), and had a hell of a time getting to sleep. When he was younger he was an escape artist and was prone to hysteria. He has recently started hand flapping when he gets excited.
Plenty of physical exercise and a gluten and caesin free diet take care of his sensory defensive issues for the most part. Melatonin takes care of getting to sleep. A host of vitamins and mineral supplements keeps him on an even keel. ABA is helping him to catch up the year he lost between 3 and 4, and occupational therapy helps a bit also.
Keep an eye on your sons ears. If they go bright red sometimes this is a pretty good indication that he is not coping with dairy or wheat in his diet.
Autism and disabled are two very big scary words which I have had to digest and accept (took me about a year to do this) but dont let fear of these words get in the way of you seeking answers and intervention for your son, who sounds to me is just mildly sensory defensive. The sooner the better, his brain is very elastic at 3 years old, and with help he can rewire neural pathways if they are a bit off more easily now than any time in his future.