Hi Mummy Chook -
Great question - I'm so excited we are here and able to offer our support. What you are describing is definitely something we have seen before and been able to help other familes with. Many of the children we work with develop sound sensitivities at some point in their program.
Often it's possible for a child's food allergies to result in sensitivities to sound - so if you're not doing so already, try looking into a gluten- and casein-free diet. If you're already doing a diet, then his sensitivity to sound may be a wonderful sign that he is emerging from his autism. Very often when our children become more and more connected to us in the world of socializing then they begin to hear new sounds. The sounds seem new or overwhelming to our children because before they were so deep into their exclusitvity and their ism that they had been blocking all of this out. So one possiblity is that your son is actually becoming more and more aware of his surroundings and more connected (an example being this increase in his eye contact).
Thank you for posting your questions!
HAVE FUN PLAYING!!