Greetings. How do I silence the sounds made when a person enters or leaves a conference via phone. Especially the loud "thud" made when leaving, it's very distracting.

You should be able to turn off the door bell (or similary named feature) with your phone bridge. This is a function of the phone bridge, not Adobe Connect. There is probably a star command to turn the feature off. If we knew what phone provider you used, then a link could be provided to their commands.

As to the loud thud, I'm not sure what you mean by that. Maybe ask your attendees to hang up gently?