i want to add that since November I have had 3 Macbook Pro 15" units and 2 Macbook Pro 17" units. All of them have had the 320 @ 7200 CTO option. Two of the 15" computers had Hitachi drives, and one had the Seagate 7200.3 Momentus. The Seagate was definitely the quietest and the best. Then the first Macbook Pro 17" had a Hitachi, which works well but is a bit louder and has regular clicking noises. The second Macbook Pro 17" came with a Seagate 7200.3 Momentus. This is the one that beeps. All the Hitachi drives click and they have a louder operational hum to them. Since they all make the same noises it doesn't bother me, and for some reason a click is more tolerable than a beep. Every notebook I've had has a clicking hard drive.
However, this latest Seagate is the identical model as the last one I had, yet this one beeps. I think there must be some kind of issue with it, although it seems to perform just fine. What I like about the Seagate drives is that they don't have the clicking that Hitachi and Samsung have. This beep/blip/whatever it is though is somehow profoundly annoying.
Summary:
5 Unibody Macbook Pros with CTO 320@7200 HDs:
3 Hitachi Travelstars - All sound the same (mild hum, clicks)
2 Seagate Momentus 7200.3 - One silent, one beeps.