Why do I hear static noise when I plug in headphones?
When using headphones or any auxiliary plug in my LG G5, I get a static hissing noise.
The static noise is most likely caused by a faulty auxiliary cord, so you can replace that quickly and for cheap. Less likely, but possible, is a faulty auxiliary cord plug in. The plug in is modular to the phone, so removing it takes only about 20 minutes with minimal tools needed. There is a guide on this LG G5 page for doing that replacement. Then you could order and replace the plug in.