This seems to be a known issue on Chrome where some peers hear an echo if the call happens without the use of an external headset. In order to always enable echo cancellation on Chrome, you can do the following steps.

01. Go to chrome://flags on your browser

02. Find the 'WebRTC Echo Canceller 3' option and click on 'Enable' 

03. Restart your browser for the changes to take effect

Other articles you may be interested in:

• Echo cancellation mangles outgoing audio when there is also incoming audio 

           (See Also : Improve AEC performance when using headset for long DT sections)

• Echo Cancellation breaks after 15+ minutes on hangout with chrome on mac