You may try making sure that the playback volume is as high as it will go on the camera by pressing the <UP> button during playback.
Also, on the front of the camera above the lens there are two small microphone holes. Please make sure nothing is obstructing them.
If the volume is still too low, your camera may need to be examined by our Factory Service Center. To start this process process, you'll need to complete a Repair Request on our website.
If this is a time sensitive-matter, additional support options are available at Contact Us.