Since I purchased my MacBook Air back in April, I've been using a Seagate External HDD to back up with Time Machine. The drive has been rock solid, and I haven't had ANY problems with it. However, just today - the drive has started randomly unmounting. After ~5 minutes of being plugged in, it just decides to quit. Oddly enough, the power light on the drive stays on after it's done unmounting itself. This doesn't usually happen when I unmount the drive manually. It's also worth mentioning that I've tried repairing the disk/permissions with Disk Utility, but the disk conviently unmounts itself before the process is completed. Is there any way to fix this, or is the drive just defective? Thanks.