Autism has many facets, and hyperacusis can be one of them. The primary things we experienced with my son was literally a physical pain for him to be exposed to loud noises, large places, crowds (small room or big room,,,too many people and noises). The sensory overload was unbearable for him.
Between the speech delay and the sensitivity to sound, get your child tested. One of the best is Dr. Christine Johnson at the Village of Hope...can be a long waiting list to get in. In the mean time, if you have not already done so, get ahold of Easter Seals, ask for them to evaluate your child, get your dr to write the referral.
Then, if you have the funds, check the internet google for auditory integration therapy/training. There is a group out of dallas that is incredible, can't remember the name, but they are based in Dallas. AIT made a huge difference after just 1 treatment day for my son. He obeyed! He heard me! He could go into HEB and not start crying. Tune ups, yes, but not often. There is no one here who has the experience or who I would trust with AIT, but there are people here who do it. But, this group in Dallas is incredible. In the mean time, don't waste time, get your child evaluated for Autism...and if there is any diagnosis on the spectrum, don't panic...yes it is scarey. But what you have already described in your son it sounds like it's just really starting to hit, if it is. If you son is interacting and responsive, you are way ahead of the game. And, there are levels of being affected. My son went from catatonic due to food allergies and intestinal problems to now being in a fully functional mainstream elementary school w/ receptive language on target and expressive not too far behind.
DON'T EVER DISCOUNT YOUR INTUITION. If you are feeling like something is not working right for your baby, PAY ATTENTION TO THOSE FEELINGS! Don't be brushed off by any doctor telling you he is fine, it's within range. And if your child is diagnosed with anything, get an OT evaluation (jeannette schwartz, Occupational Therapy Services) and keep up your attention to your son. If your baby is evaluated and declared just to be a normal little boy, remember, little boys are like klingons to Moms....they are entirely different creatures and you will be very busy! Read whatever you can by David Guerian (he writes a lot of books about boys learning differences etc) and just enjoy the ride...mine are a hoot, and I don't know what I would do without them! Pure entertianment, frustration, grey hair causing boys, but they are charmers who are full of love!
Good luck!