Even though you were monitoring the sound and watching the meters, it’s easily possible to overdrive the recording on certain sounds. Many sounds which are short in nature or in the higher frequency ranges will over modulate a recording and cause distortion, espically with a digital format camera. These sounds can simply be too short in nature to give the meters a chance to react properly. Many camcorders will have the Vu meters damped a bit to show more of an average level, but they will not respond quickly enough to show the very short, but very “loud” peaks present in your material. Most professional field mixers will include both a “peak hold” option on the meters to indicate the loudest part of a sound and also a red (usually) peak indicator that has a very fast response time. I’ve actually recorded Native American dances locally here and I’ve seen my peak light on my mixer lighting up like a string of Christmas lights while the slower, averaging meter on the mixer showing levels in the normal range. Even though your waveforms look OK, clipping could have easily occured in the recording process. The waveforms in FCP while useful, are not terribly accurate and lack the detail that many professional sound processing programs can provide. Your recording was most likely over driven while recording and the waveforms lack sufficient details to show it clearly. In the future, use a good mixer (both electronic and human) and err on the side of bringing the audio down a little more. You can always bring it up and add a bit of compresser to it.
Once it’s clipped, there’s not a lot you can do to fix it.
Tom