something i have found but the general message is the same:

from: http://preview.videosystems.com/news...ing_bad_audio/

Distortion and Clicks

Audio distortion is the worst of the problems, and the most intractable. Distortion occurs when an audio input is too loud for the input of the next stage to reproduce cleanly. Consequently the tops of the audio waveforms are clipped off, hence the term "clipping". Distortion generally imparts a "raspy" quality to the sound, and in extreme cases can make your sound unintelligible. While analog distortion is the most common, digital devices are also susceptible to distortion. Analog devices distort in a gradual fashion as gain is increased, but when digital devices distort they do so at one particular threshold level, and the result is instant unpleasantness.

The best way to eliminate distortion is to prevent it before it happens. There are few remedies for distortion once the recording is done, especially in extreme cases. If the amount of distortion is slight or the distorted segments are short, then you can use your software audio editor's Pencil Tool to literally draw smooth tops on the waveforms.
But if the distortion is severe or prolonged and there's no chance of re-recording the sound, you may be best served by taking your distorted audio files to a facility that has Sonic Solutions' NoNoise, which is part of their Sonic Studio HD product http://www.sonic.com/sshd_home.html.

NoNoise is a venerable computer program specifically designed to eliminate unwanted noises from audio recordings, and it is particularly effective when dealing with distortion. It can even generate resynthesized audio to replace damaged sound. NoNoise is also your best choice for dealing with dynamic noise that does not respond to filtering. It is the industry standard in noise elimination, but a NoNoise system comes with a hefty price tag, so it's best to farm this work out. Depending on where you live, expect to pay anywhere from $60/hour to $150/hr for NoNoise work. Your budget may not like it but sometimes there is no other option.