I have cleaned up the sound portion of video clips easily, using Audacity.
But only when I have no interest in the video portion.
After the cleanup, you have to re-save or export the altered file, and Audacity won't export video as far as I know.
So I end up with the improved sound in an audio file, no video. Which is fine with me, all I wanted was the audio anyway.
I assume you could export the Audacity-altered sound portion and then "paste" that sound track over the original noisy sound track in the video, using a video editor of some type. I've never done it.
I'm not sure of the sound improvement capabilities found in video editors. I've used video editors, but never to alter the sound track of a video clip.
The basic video editors I have used can convert the audio portion to some other format, but cannot reduce noise, clicks, pops, etc like Audacity.
You might use Audacity and try the "paste" method mentioned above---you'd have to find a basic video editor that will let you over-write an existing sound track with your altered one.
There may be a higher quality video editor that includes audio noise reduction, but you may have to pay for it.
Search out expertise on forums devoted to video.
Audacity is here: http://audacity.sourceforge.net/download/
It is often regarded as the best free sound editor for the PC.