Like I said, if you're experiencing excess noise when playing back DVDs then there is something wrong.
The drive is only noisy for me whenever I've got an Installer Disc in there such as a Windows XP CD or a Windows Vista DVD. But then again, I suppose the drive is supposed to spin-up and spin-down several times during a Windows installation.
I suspect that the problem with your drive is that it doesn't spin down correctly which is the reason why you hear so much noise coming from your drive. I think you'll agree that this is a defect and you should try to get a replacement drive (if possible).