The issue is caused when the microphone being used is able to hear the sound coming from the speakers. This is often due to a slow internet upload speed or the volume being turned up too loud.
Try the following steps to resolve this issue:
Turn down your volume on your computer
Use a pair of headphones or earbuds that are equipped with a microphone to eliminate outside noise. Most modern style earbuds, like the ones that come with your phone, will work.
Ensure that your computer is using the correct input for your headset. This can be checked by accessing the sound options on the computer (On PC: Settings>Sound / On Mac: Preferences>Sound). If the headset is not listed as your default audio device for inputs and outputs, make sure to disable the other device and make the headset your default.
You'll need to refresh your video session after making changes to sound settings.
Consult with your computer manufacturer with additional questions about this.
Ensure that no other applications are open and using the microphone at the same time. (i.e. Skype, Facetime, etc…)