This issue is caused when EBS is configured with an audio source that also has participant audio traveling through it.
If you are using a PC, you must video conference on a separate computer or connect a different audio output specifically for Evercast participant audio (i.e. USB Speakers).
If you have USB speakers, change the speaker output of your Evercast session by clicking the headphone icon (device selector) and selecting your alternative speaker output.
If you experience this problem and you're using a Mac along with Loopback, make sure Chrome isn't selected as a Loopback source.