Way to prevent the noise when 2 phones together In using an app, for example Wechat, to have video chats.

Two Android phones A and B are sitting in the same room. The two users of A and B stated video chat with mobile phones C and D in another city, when two users of C and D are also sitting in the same room.

That is, phone A is calling phone C; phone B is calling phone D.

When the video chats started, because phones A and B,  C and D are close to each other, sharp noises started to appear.

What's the way to prevent this noises in the video chats?

Thank you.
This phenomenon is called audio feedback which usually occurs when the sound from the speakers reaches back into the microphone, and then gets amplified because of the speaker-mic loop.

Common and general solutions are to cut off the loop, or at least reduce the loop gain by:


Wearing earphone or headphone (isolate the speaker and the mic, prevent the feedback loop completely)
Mute the mic when not needed to speak (prevent the chance of feedback loop)
Reduce the speaker volume (reduce the volume gain)
Take some distance between the speakers (reduce the volume gain)