Improving the quality of sound recordings in post production can be done in Final Cut Pro X, by using the audio functions in the inspection window. If this does not work you can try cleaning hiss, electrical hum or air conditioning noise in a program called Audacity. This can make your sound more even over the edits by removing background noises. This video will show you how.
Be aware that not all sound can be cleaned nor all noises removed. You should always do your best to record sound in a location with no background noises and monitor recording levels using head phones and checking recording after each recording by playing back.