Problem with microphone

[Guest bsketball]

Often when I call somebody, they have a very hard time hearing me. It happens about 1 out of 3 of my phone calls. I speak very loudly into my microphone, but they can barely hear what I'm saying. I tried updating my phone to the latest version, but it still does this.

Because it only happens some of the time, I doubt it is a hardware issue. But even after updating, it still happens. Does anybody know what it is and how to fix it?