in FCP, i use the 3 Band EQ.
drop it onto the clip in the timeline, double click it into the viewer, and go to the Filters tab.
if the offending noise in the bass, like a low rumble,
lift the bass gain UP all the way,
work the frequency slider till you MAXIMISE the offending sound.
now that you have zeroed in on it, bring the gain back down till you minimize the sound without affecting the voice too much.
mid range noises will probably intersect with the voice too much,
but you can try it and see how you go.
oh, if you have been using the audio mix tool to record audio keyframes,
then you will also record all the tweaking you do in the audio filters, too.
i like to add the "record Audio Keyframes" button to the viewer for this reason.
cheers,
nick