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 'Enable Delay Agnostic AEC in WebRTC' option and click on 'Enable

03. Restart your browser for the changes to take effect

For more references regarding echo cancellation on Chrome, you can also take a look at the following issues raised on google : 

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