Can't say about 1650 as it still hasn't arrived yet. I can only compare 1620 and 1640. 1640 overall is actually slightly quiter, however the sound has some sort of high frequency pitch mixed in, so when it's burning at full speed subjectively it sounds more annoying to my ears. When I'm watching DVDs I can't tell any difference between two, both are extremely quiet. Are you sure your 1650 slows down when watching DVDs? If not try using nero drive speed, it works magic.