All the iMacs in my local Apple store are Seagate, and as far as for Apples official line, its not an issue.
http://support.apple.com/kb/TS3204 its how the drive sounds, now since I know PC's that have this noise and the same drives but with different firmware and are still going I'm not worrying, Apple computers are mass produced units after all.
People expect far to much for the money, you are paying for the Apple brand, we all know that. If you buy a hand built PC fair enough complain, go get a windows 7 PC built to your spec at half the price with USB 3 Sata 6 and an i7 or your choice if you want, and get solid state drives. The iMac is is a mass produced AIO, yes quality is not great sometimes, but they sell tens of thousands of these things and many people do not issue with Seagate drives, in fact many have the same exact noise with WD and Hitachi on here, some even have silent Seagate's so you cannot just say one drive is better with Apple as its a lottery really.
If you sit and listen to your hard drive seek and it bugs then change it over and over if you like, but most stores even Apple online I imagine will reach a limit and give you a refund in the end, as you are chewing though stock they could sell to others. Yes change your hard drive by Apple tech support and you could get yet another Seagate/WD/Hitachi that's noisy.
I don't hear mine, I tuned out I guess and I am just enjoying my computer. Since Apple have used these drives since late 2009 I can't see mass failure issues on the forum.
Just enjoy your Mac and stop thinking its built for you out of love and magic, its not.
Message was edited by: killhippie