Higher capacity drive of the same generation and brand are usually a bit noisier and warmer since a low capacity drive has fewer platters than a high capacity drive. The capacity borders between the number of platters varies between brands, models and over time.
anyways HD noise doesn't depend on the size, its the speed that matter. try slowing it down a little the noise should decrease.
also check if ur HD is properly screwd into the HD rack make sure the screws are tight, also its a good idea to use rubber o-rings between the screw and the hole.
The 200GB HD is noisier (by about 25%) on all three accounts you mentioned than the 80GB HD but there is no screeching etc.
Both HDs are very secure in the PC hence vibration free and I have analysed the sound using my USB 2 enclosure while the top case is removed (its a ICY BOX) while connected to my laptop so the sound isn't confused/mixed in with the fan noise of my PC.
Ep, glad to see you come back and tidy up...did want to ask a one day favor, I want to enhance my resume , was hoping you could make me administrator for a day, if so, take me right off since I won't be here to do anything, and don't know the slightest about the board, but it would be nice putting "served administrator osnn", if can do, THANKS