Most consumer MiniDV camcorders won't let you set sound levels manually. The camera has a built-in sound limiter that keeps the audio signal from distorting to tape. The audio limiter is used as a protective device for the camera, but it can work against you as well.
For example, a sudden loud noise will cause the camera's sound limiter to kick in, making your sound levels suddenly drop across the board. This is a big concern in interview situations where a word may abruptly be dropped out in midsentence.
If you're taping an interview and a car backfires or a door is suddenly slammed shut, you may want to ask the person to repeat what he or she was saying, just to be on the safe side.