For your reference, here are some troubleshooting steps:
1. The sound of live video is turned off by default in the Mi Home/Xiaomi Home APP, you can turn it on by the volume button in the video window of the Mi Home/Xiaomi Home APP, you can turn up the volume on your phone if the volume is low;
2. If there is noise in the live video, please keep your phone away from the camera and avoid placing the camera next to electronic devices like refrigerators and microwave ovens;
3. If the device is placed in a high place or the lens is facing down, it will cause the microphone to be buried in the camera body and make echoes when it receives sounds from the speaker, you need to move the microphone out of the camera body in this case.
We hope the above methods can help you solve the problem. If your problem still exists, please contact the local after-sales service center for further assistance.