Yes, what Martin says is true, at least of Soundsoap. When you tell it to find the noise it tends to overdo it, making the voice remaining sound hollow, as if spoken through a tube or over the phone. You must be patient and tweak the thing to get it right. Also, I tend to do a “save as” with it and add 1 or something to the original file name, then you can save all the original clips somewhere else, remove the 1 or whatever from the new clips and reconnect the media. That way, you still have the originals should you want to change anything.
Yes, I know Soundtrack Pro can do this non-destructively, but I just like Soundsoap much better for noise reduction. Have not had as good an experience with Soundtrack.