I had the same problem when I had my daughter.
My son with ASD is only 18 months older, but it was like this for many years.
He did not want anything to do with her, if I was holding her he would come and start hitting her.
Unfortunately this continued for many years, I could not trust to even turn my back for a second.
As he got older I taught him ways to get away from the noise, by going to his room, we even had specialized ear plugs made that helped bring noise down to normal level.
It is just a sensory issue and you just need to find what will work for your situation.
My children are 13 and 12 now and he still can get bothered when his sister is a bit crabby. He handles it much better now.

It will just take time.

Yes it is overwhelming for my son. I got him noise canceling headphones best investment I have ever made and he has his own personal get away space and it really is for the best. And I am glad we have done that for him.