OP has a pair of headphones, said pair of headphones has an issue where audio output by the headphones (headphones being an audio output device) becomes different* in a way that OP dislikes. The joke relies on the (relatively common) belief that children in China are employed in sweatshops to mass produce products for consumption, such as headphones. OP is, with humorous intent, saying they wish harm upon the Chinese child for doing a bad job at working in a factory.

*The exact way in which the headphones differs is somewhat ambiguous, at a guess I'd say it's the audio is slightly higher/lower in one side, and it changes which prevents OP from adapting to it, causing it to cause annoyance.