Seagate makes some decent drives. However in the past year or so, all their new drives make very annoying "diagnostic" read noises every couple of seconds. When I wanted a silent drive for my fanless iMac, everyone recommended a Seagate, so thats what I got. But I quickly noticed that every couple of seconds when the drive is idle, it makes this very annoying "chattering" sound. I thought it was a defective drive, but when I checked online forums, I wasn't the only one! I called Seagate and they explained this is a self test that the drive does, and is normal operation.
Not satisfied with that, I quickly sent the drive back and got a Samsung instead. The Samsung was even more quiet, and had no annoying sounds.