Participant echo and feedback Host no echo

Hello 

I’m reaching out regarding a technical issue we encountered during a recent webinar hosted by our company, and I’m hoping to get some assistance in resolving it for future sessions.

Here’s a summary of the issue:

• Whenever our executive, who served as the webinar host, unmuted themselves to speak, participants experienced significant feedback and echo.
• This occurred even though all participants were muted during the session.
• The webinar host did not personally experience any feedback or echo on their end while speaking.
• The host was using a laptop with built-in speakers and a built-in microphone in a private office environment.

Given that participants were muted, we’re unsure what might have caused the feedback. Please help in diagnosing and resolving this issue to ensure a smooth experience for all attendees in the future. I've looked at other articles on audio feedback resulting from a second device picking up sound but per the webinar host this wasn't the issue.