There was a program for ripping called Audiograbber. It is abandonware now, so downloads are free. Fortunately, it will work on more modern Windows based operating systems. I mention it because the program had an optional noise removal plugin made by Algorithmix that was very inexpensive.
The plugin allowed for correction before the audio was processed. It worked sort of like a tape monitor switch. The user could tweak various parameters to get the best out of the software without losing the desired audio. For the few remaining artifacts, Soundforge could be used on the processed file. Maybe an inquiry will get you the plugin.
If it still exists, this may be a halfway decent solution to your problem. It's a thought, anyway.
EDIT: I assume you are going to strip the audio from the mpeg4? My idea won't work with video files.