Me too, constant loud static from a new Express. This has been widely discussed here for years and for all Roku models. This is what helped me reduce it to tolerable levels via audio settings:.
1) turn menu volume to off.
2) set audio mode to stereo.
3) (in my case) set Hdmi mode to PCM-stereo.
Now I get a mild static burst only when the app that's playing switches between content streams e.g. for an ad. and it's now at an acceptable level of annoyance. This never happened with Fire Stick.