Why am I getting poor audio quality on playbacks?

This camera didn't come with a great microphone, which makes recording quality audio difficult. Make sure when you record that there's nothing obstructing the microphone and speaker. The speaker is on the side of the camera where the screen flips out from, and the microphone is on the top of the camera above the lens. Also check the audio levels or volume to see if that affects playback.

If nothing is blocking the speaker or microphone and you don't think that your audio levels are affecting the quality of playback, then your microphone might be damaged. iFixit provides a guide for getting to it and replacing it. Samsung HMX-QF20 Troubleshooting

Since this unit records to a flash drive, the media itself is not the issue. I would check on the condition of the windscreen for the mic. If this has deteriorated, it may be blocking the mic itself and causing a muffled sound. Other than that, the problem would be in the analog to digital circuitry that would take further investigation and testing to locate and resolve.

Dan