I feel your DS' pain.
There is a particular SPD-related
thing that this sounds an awful lot like...
mine started about the same age. Now, I have hyper-sensorial phenomena/awareness in a number of dimensions (auditory is just one)-- but clicking, tapping, crunching, rustling, crinkling, chewing-- it's hellish* and yes that IS the word that I use.
This might be the onset of something called Misophonia. Just something to be aware of, as it isn't exactly the same as hyperacusis (though I have that as well, I think). I do NOT actually find earplugs/sound
isolation to be as effective for me personally as an effective
masking of the noise.
In some situations, however, earplugs (or just a cotton ball that you can quickly pull a couple of bits off of from a pocket) can make things tolerable. Use of headphones may not always be acceptable.
* go ahead, ASK ME how much I liked doing my subject GRE in an icy room with three other people-- one a gum SMACKER, one with a flaming head cold and a box of tissues and cough drops, and the other one of those fidgety people, equipped with a damned clicky-clicky retractable eraser?? One of the worst sensory memories of my entire life.
