I have been following this topic on and off since getting my new iMac (the i5 27" Quad-core) but have not yet seen any real answers to the topic at hand.
I have noticed, since day 1, a relatively loud HD read/write noise on this new iMac which my old 20" (white iMac '06) did not make at all. My old iMac opening Photoshop is quieter than my new one just sitting idle. It's not right.
For the benefit of everyone here, I've tried my hardest to record the noise whilst opening a few applications. Please turn up your volume *a lot*(!) it's quite a poor recording from my iPhone 4 but it's the best I can personally create with the tools I've got. You can hear my mouse clicks too which helps time the read/write noise.
The recording:
http://bit.ly/bPRpSZ
So, is this normal? That noise occurs when idle, but only in the 'Pak Pak' manner several other people have mentioned. It's the same tone, just a different tempo when idle - about 2 'clicks' or 'paks' per 10-30 seconds.
Do I take the iMac back to Apple, or have I just got myself another one of Apple's new, erhmm, professional products?