Also add to TOSHIBAer's post: Are these playback issues while you view them on a stand alone player,or viewing them on your pc?
Verify them: If those issues occur while viewing on a stand alone player: Take note of the areas where the issues occur. Then play that backup in your pc,using the same dvd-rw drive that produced it-to play it.Keep a close eye on that area when issues occur. A burner must be able to play it's own backups,and they should look near original in quality.
Also test in some friends/family members/or next door neighbors players. The more,then the better.That'll give you a better perspective as to which drives or all drives having issues with that backup.
Brand name/format/and disc speed of blank media? MID code would be handy.
How fast were they burned?
Did you multi-task during the backup process?
Hard drives defragged?
Using Paper/sticker labels?