I have a Oneplus 8 pro.
There is notable static/hissing when listening using USB C Headphones (no headphone jack).
The worst part is, its not constant.
When I am on a youtube video or a call, when the other person stops talking the hissing lasts for 1-2 seconds after they stop talking. Then when they start talking it comes back.
Its like a constant on again off again kinda thing.
I bought the phone from Kogan and wondering whether to send it away for 2+ weeks for them to look at.
Had it for about a month. Didn't notice it before (though I haven't been using a USB C headphones much before.
The static ("noise floor") is a property of the DAC (audio chip) used in the headphones. Try other headphones. The phone outputs digital audio to the headphones, the headphones are responsible for making the sound.