Hi there,
just a tip: while trying to improve the quality of files I recently posted I came accross a (for me?) new Mac SW tool that works pretty nicely for me. Dead simple to operate, with very good results. Both in removing noise but also in boosting the sound level (without adding too much noise again).
SW is called SoundSoap Solo and can be downloaded from the Apple App Store. Works with videos as well as with audio-only files.
Cheers and a happy new year to everybody!
Muffe