The microphone is malfunctioning.

If the microphone adds noise that makes it difficult for others to understand you during phone calls, try the following:
1. Ensure that you have the latest firmware installed.
2. Record audio and playback to test the mics.
3. Check and confirm that no dirt is blocking any of the 3 microphones.
4. Disconnect and reconnect the earbuds.
5. Reset the device.