clik sounds in audio track when editing effects

When I was editing some automation effect on a vocal track, I discovered clicks coming from nowhere. It was as the audio track is being corrupted during the altering. The click sound does not go away, even after undoing the altering and removing the effects. Only option is to insert the audiofile again. Does anyone know about this. From now on, I make a copy of the track underneath, so I can insert it again, if the audiofile gets corrupted. I do not understand, why this happens. Anyone?