Normally, I'd say it sounds like a dropframe/non-dropframe issue - BUT I do remember having some trouble with using the quicktime conversion to convert video footage - the problem can end up where it guesses wrong on your timebase. If you go into your quicktime conversion, and on the video portion, click settings - and where it says Framerate - most likely it currently is set to "Current" - change that to what your video frame rate really is (most likely 29.97 or 59.94) and re-export and see what happens.
You can tell what your frame rate is set to - if you look at your project area, where it shows the sequence and the video capture files, if you scroll across that table, you'll se a section that states Vid Rate; that number *should* be accurate, and usually is the same between the video source files and your sequence.
ps - what you're referring to is an audio sync problem (or audio / video sync issue) - not a clipping issue. When people refer to clipping issues - they are referring to audio exceeding maximum levels causing a flattop on waveforms - hence clipping the tops and/or bottoms of audio. This might help explain it a bit better:
http://en.wikipedia.org/wiki/Clipping_(audio) - otherwise, your title would have been clearer with - audio going out of sync with video when exported.
