I think the most simple and logical answer would be “dying,” but this seems a little unusual. I have a Mac Mini with an Iomega external 500gb hard drive. The hard drive is making noise; not the death-clicks indicative of a hard drive on its way out, but the noise you usually hear when it’s reading/writing. But it’s constant. My OS X Activity Monitor shows constant spikes in reads/writes. Movies being played off the drive started skipping in VLC. So I figured it was caused by some rogue software monopolizing the drive.
So I put my Mac to sleep…and the noise continued. I turned the drive off all night & disconnected its firewire cable from the Mac. Turned it on this morning and it’s still making noise. Is there anything built into an external enclosure, or the drive itself, that would cause it to chunk away even without input from the computer?
Here’s a WAG: The only reason I can think of for a drive making read/write sounds while not hooked up to a computer is that it is constantly experiencing errors reading blocks, and trying to move the data in them to blocks that it thinks aren’t bad. If this is the case, then you’re eventually going to run out of good blocks, and the drive will fail.
It might be possible to interrogate the disk and ask it if this is what it is doing, possibly using some SMART utility, but I don’t know about doing that to a USB/Firewire connected drive - Disk Utility on the Mac does show the SMART status for the internal drives at least.