look for the old beta version of adobe audition. It's EXACTLY like the retail version.
Export the audio into a wave file (not avi...duh) then open it up into adobe audition. Or find an old version of cool edit 96 or better. Both programs are the same (adobe bought cool edit and redid the software)
Now, go a part of the wave where YOU ONLY HEAR BUZZ. No voices, just buzz. this may not even be a second long. zoom in and everything to get as isolated a clip as possible. With this highlighted, goto effects, then noise reduction, and click "get profile from selection" then click close, not "ok" not "cancel" but CLOSE.
Then select the entire wave. (CTRL A) and go back to noise reduction, and then just click ok. It'll clean it up, and you should be surprised.
If your voices sound liek their underwater, find a better, quieter place where there's a camera buzz that you want out.
WHat you're doing is showing the computer what the data for a buzz looks like. then it takes it, looks for it among good sound, and deletes it, saving the good sound. Often, it accidentally picks out a bit of the vocals and makes it sound all underwatery. Takes a little bit of practice, but the results can be near perfect.
You may want to compress your audio once you're done (not compress the file into mp3, but compress the volume of the audio in case you're unsure of what compress I'm talking about) so that your audio levels are all equal, and your audience isn't surprised when you suddenly get too loud, or too quiet.