before someone posts "buy a ps3".. its normal, bothered me so much I got a cheepy dvd player to watch movies on. The new BenQ drives are better than the old one's but it still sounds like its taking off!
a) dvd firmware flash (instead of normal 12X, it runs 8X [recommended]) Voids the warranty, chance of getting Live banned in the future, and makes you a pirate ...
b) buy a new xbox 360 with benq drive (a little quiter) or wait for next shipment of 360s as they will have the LiteOn DG-16D2S DVD drive (not confirmed but has been seen in refurbished Australian consoles)
I watch movies on the xbox and don't hear a thing - its really not that bad.
I did have one xbox that the dvd sounded like someone was using a chainsaw on a flock of sheep, but had that one exchanged...maybe you have a faulty drive?