The "300" G hard drive of my new PC is otherwise rather silent, but when it reads and writes, it makes quite an irritating sound. It's interesting that I only notice the sound when I do "saMyama" on it. Some reading and/or writing seems to be happening almost all the time, even when no application is running. Of course there are some 50 processes running, but checking the task manager doesn't seem to indicate, at least most of the time, other activity than the System Idle process.
The drive is Seagate. I've been quite satisfied with most of my previous Seagates. For instance one 40 G Barracuda is so silent that the reading/writing is barely noticeable. I wonder if for instance a Western Digital is nowadays more silent than a Seagate.