Earplugs have helped me with some aspects of CAPD. I used to wear earplugs sometimes because of my hyperacute hearing, and they were the kind you buy in the store. They made a constant crinkling and rubbing noise that made it difficult to hear anything.

I now wear what are called "musician's earplugs" which are great because they are custom-fitted, not made of crinkly material, and smooth. They block out sound better. Also, they come with filters. The filters filter out sounds in various frequency ranges, making it so that speech sound usually sounds about right, with background noise diminished. These are more expensive but also more comfortable and more effective. They help me screen out background noise.

A warning about earplugs -- if you have hyperacute hearing, and you wear them all the time, your hearing may "adjust" and then be even more hyperacute and painful when you take them off. That is why it is important only to wear earplugs when absolutely necessary.