My wife had this trubble, it was from a small amount of rain water that got into the microphone and killed it. The fix is to take the device apart, desoder the microphone, soder in a new microphone and put the device back to gather. HTC refused to honor the warenty then they voided the warenty wich forced me to fix it after they charged us $147.97 just for the microphone, the phone was only a $65 device. My advice, save the trubble, put it in the bone yard and enjoy a new device.