Start WebRTC viewer with Voice Chat unchecked and Microphone is use by: SecondLifeViewer will appear in the taskbar.
This causes sound issues for people who don't regularly use voice and are using bluetooth headphones as it splits the bandwidth between input and output channels and renders the sound at a lower quality.
I believe this might be the root cause of this other canny report as well: https://feedback.secondlife.com/bug-reports/p/new-release-screws-up-my-sound