How is your Hitachi drive? Is it quiet? I do not mean the drive itself, but the system overall? I just returned mine because the fan was loud and I have heard that all new iMacs with 2TB Hitachi drives have the same issue.
I have the 2 Tb Hitachi-mine has a low hum. The funny thing is if I tilt the iMac all the way down the humming ends. Tilt the iMac up and the humming gets more noticeable. Weird.
I've always had WDC HDD's-never has any sort of problems/annoyances.