I have encountered issues occasionally during my year of video recording, most of them have been audio related and not easy to notice until after the recording has finished. It could be a noise in the background, or it could be a fault with the mic. What I found to resolve this is using an external mic that I attach to the collar of the subject, this allows the camera to be a secondary audio recording device to the external mic and solved my issues. I found that just using the camera mic means if the audio is no good then the video can be ruined.
For issues with sound that can be fixed, I usually edit audio in Audacity (audio editing tool). I can remove unwanted noise and amplify audio where needed or for simple audio edits I use After Effects.
Editing an audio file in Audacity
An external mic attached to collar
