To prevent feedback, if you have participants in the same room as the Chromebox joining with their laptops (to present content or screenshare to the CfM) they will need to be muted or the audio input on the laptops disabled. Multiple audio input devices in the same room will cause a feedback echo. If they are participants joining from a laptop outside of the conference room, and you are getting feedback from them, the built-in laptop mic audio level may need to be adjusted.