Ok, what I believe is happening is ripped CD's are creating their own playlist for media players in their ripped folders.
On my PC what I did is right clicked the start menu, clicked "explore" and found the folder all of my songs and folders were in. Then I searched (upper right corner says "search") within the folder for "m3u", just because the playlist does not say ".m3u" at the end of it the search will still locate the files. I then shift-deleted all the files, click the first file hold shift and click the last file, right click and delete. Then went back to iTunes and added all my songs.
I know you are on Mac but it isn't much of a difference, same concept. Locate main music folder and search for all the "m3u" files.
Also make sure you DO NOT delete the playlist that you WANT to keep if they are all in the same location. You can prevent this by NOT doing an overall search for "m3u" files.
Sorry if this is overly detailed, but I know some people are just not so tech savy. But I hope this helps everyone!
Scott