I have an external HD (WD 2TB My Passport Ultra) that I use with my Mac for Time Machine backup. Everything is working fine. An oddity though: When I eject the drive, the Mac has no complaints, but usually (always?) the HD activity light will continue blinking "for a while" and I can hear the HD heads scurrying back and forth across the platters. Eventually, it quiets down. This all happens when the drive is unmounted, but still connected to the Mac (Disk Utility still shows its existence.) What is happening here? Anything to be concerned about? Do I run the risk of HD corruption if I unplug (and therefore power down) before the drive heads are "quiet"? Something else going on?