Cause: This will happen if the mic picks up sound from within the meeting room which then creates feedback. If you're using external speakers (as in a conference environment), their system might generate disruptive echo that will interfere with the interview flow.
Solution: Please use headphones. If using a headset is not an option, you might try selectively muting participant microphones to determine which computer is the cause. Another cause may be multiple instances of the meeting room in multiple tabs.
Don't run two clients in the same physical room (sound from the speaker on one computer enters the microphone of the other computer).
Reduce the speaker volume.
Use a headset.
Use a conference microphone/speaker with built-in noise canceling.