Why in the world do some individuals with autism feel great about being loud themselves but balk at the slightest noise from others? How frustrating! How confusing!
The answer is relatively simple. Many on the spectrum feel very sensitive to unexpected noises or unexpected qualities of sound (like rhythm or pitch). Some are very specific about not wanting to hear particular syncopations or volume shifts. When the autistic individual is creating the sounds, his brain expects each one. There is no startle response or upsetting combination of tones.
The same is true for listening preferences for music or other media. The autistic will often choose things to listen to that are repetitive and predictable, or that fall into a known genre.
"Why, why, why does the individual on the spectrum insist in that way?" we may ask. It seems unreasonable, picky, and controlling. But ask yourself why you loathe the noise of nails on a chalkboard. Most of us can't stand the sound. At the same time, it's much harder to explain why. Our brains don't like it. It's as confusing and straightforward as that.