a solution that can be used to fix or repair a nokia X3 with a mouthpiece microphone problem.
If encountered to troubleshoot this problem you may need to first check the microphone module and ensure that it is still working or not. Replace it if already faulty or damaged. Ensure also that the mic terminal and contact pads is properly in-tack and free from dust .dirt and oxidation build up.
If the mic module is already been replaced and still the problem occurred. you may refer this solution below for it shows certain components on nokia X3 PCB board that holds the microphones connection.
Nokia X3-00 mic, microphone solution
Just near the microphone's terminal contact pads on the PCB board, which where the filter coils and capacitors being mounted, you may need to check these components and replace if found faulty or damaged.