How to fix audio in flv files

[Rebel1]

I often d/l clips from youtube and other sites, using Firefox and a download helper. I usually have three audio problems: too loud or soft; not in sync with the video (sometimes a second or two off); and background rumble or buzz. All these problems are inherent in the clip, not originating in FF or the download helper.

Any suggestions for programs, preferably freeware, to deal with these problems? I have Cool Edit Pro as an audio editor, which I could use to record in real time (that is, a 60-minute clip would take 60 minutes to record) the sound track, then adjust volume and remove background garbage, but I don't know how I would replace the original track with this one, and sync it with the video.

Thanks,

Ray

[Rebel1]

I should have added that the audio is out of sync by a constant amount for the duration of the clip.