@MontyWales: Please can you confirm the model name and current Android version of your device, located in Settings > About phone > Model name (towards the top of the screen) > Software information > Android version.
Is the issue occurring in a specific location, or is it persistent? If you head to the Samsung Members app > Press and hold on the app icon > Diagnostics > Mic, and run through the on-screen instructions, does this flag any issues? In the meantime, please restart your phone to refresh the software, as this will address any temporary issues that may be a contributing factor. I also recommend removing any cases/covers from the device, just in case it is interfering with the internal mic.
