If the problem is not coming from your (or your correspondent's) network reception quality, you can try following this procedure to change the phone settings for the Echo Canceller/Noise Canceller (EC/NC) mode, which reduces echo and noise in phone call conversations:
IMPORTANT: The following procedure may differ depending on the product. If model-specific information is required to complete any of the steps in this solution, refer to the operating instructions supplied with the product.
- Press and hold the MIC button during a call.
- Set the mode to EC/NC-1 or EC/NC-2 to adjust.
NOTE: Surrounding noise will interfere with the microphone. Try to reduce the surrounding noise as much as possible. Roll up windows, turn down the air conditioner, etc.