Some people who use HTC One M9 report that they got problem with their device sound and audio. They find that their HTC One M9 sound or audio is not working. In other case, the HTC One M9 or HTC One M9 Plus owners find that their sound or audio is working but there are some problems on the sound or the audio.
They stated that sometimes, they cannot hear the caller voice from their microphone during calls, or the voice is distorted randomly. There are some options as the potential solution to overcome this problem as the following explanations.
One of the potential solutions to your problem is by turning off your phone, then please remove the SIM card and then reinsert the SIM card on. Please turn on the smartphone again, and see whether there is difference after this action.
Other things that may cause your problem are the dirt, debris, or dust that stuck in the microphone. Please clean it gently using the compressed air and check to see if your problem is fixed already.
Other thing you can try to fix your problem is by turning off your Bleutooth connection, because it can disturb your sound and audio problem on your phone. You can try to use your phone again after taking this action, and see if there is any difference after it.
You also can try to wipe cache partition of your HTC One M9 to fix this problem. Please turn off your HTC One M9 and please hold the Power off, Volume up, and Home button together for several second.
You will see an Android icon appear at the screen, please use Volume down to highlight wipe cache partition option, and press the Power button to select it.
Please highlight Yes using the Volume down, and then use the Power button to select it. When the process is complete, you can select Reboot System now to reboot your device.