Remove noise from video

If you are saying that you've stripped the audio from a video, noise reduced it and now want to replace it, then you can't do this in Audition - you have to use Premiere at present. You should have seen a message like this:

There are plenty of tutorials available to show you how to do this. It used to be possible to do this directly in Audition, but only in a limited number of formats, and the option hasn't been present for a while now - it has to be done externally.