I installed my first Seagate disk yesterday and after reading your post in this board i can say that it could be the english translation of what i had written in an italian board after testing the hd. I noticed the same thing you're describing in your post..
Looking for informations about that very audible idle scan, i found out that it should be a sort of "hd saver" that moves the hd heads to prevent them to stay too long in the same place, avoiding the formation of heat on the disk surface. So this is to improve reliability, but in my opinion it's a too excessive measure because you can't let your drive idle that it starts making so much noise that it seems to be in the middle of a defragmentation
There's a workaround for this: you have to avoid the hd to stay too long in idle. Maybe installing the os on it will be enough, however you can also put on one of its partitions a log that is updated often, and that's exaclty what i did with the motherboard monitor log that is written to disk every 30 seconds.
Unluckily, in my opinion there's a second problem that you haven't noticed or maybe that just doesn't bother you. I'm talking of the lack of Automatic Acoustic Management (AAM) support, that leads to a very audible noise of the drive heads in seeking. It seems that Seagate, due to copyright problems, has disabled the automatic acoustic management control in their newest hard drives and that these new models are factory set to performance mode rather than silent mode. I have been looking for informations on this too, but this time i haven't found any workaround. At the moment there seems to be no "known" way to control the acoustic management of the drive and Seagate says through their support service that aam is no longer supported.
In the end i'm wondering how two important things like these have gone unnoticed in the drive review, where it is said that the drive in idle is very silent. That's indeed true, but the problem is that the hd simply won't stay idle, but it will keep moving its heads as a sort of "hd-saver". Maybe the idle noise test has been made with the data cable unplugged, because it seems to me, even if i'm not 100% sure, that if only power is attached the disk-saver is disabled and the idle is really idle.
Greetz from Italy and sorry if i haven't been always clear with my english !!