Clacking hard drive-- why?

[ho'ard]

My MDD was making a repetitive clacking during startup. I was viewing a video and it started in the middle. holding things up a few times.
I ran Disk utility on all the drives and it seems there was a problem with the startup drive-- it took a few times but it's all checking out OK now and the clacking seems to be gone.

So, I'm wondering--

What causes the clacking? It's like a clack-clack, clack-clack, clack clack . . .

How does the repair utility work exactly, i.e. why does it give you error messages and say it can't repair something, and then seemingly at random suddenly repair the problem upon the 3rd or 5th attempt?

My "little men" theory works most of the time, but occasionally I long for a deeper understanding . . .

[ho'ard]

BTW the startup clacking has been going on for weeks or months . . . never noticed problems once up and running.

[Forrest]

Sounds like the hard drive might be failing - backup your data NOW. When you run Disk Utility - what's the SMART status? Might be a good idea to install SMARTreport on your computer - which will continuously monitor the SMART status http://homepage.mac.com/julianmayer/smar...index.html

[ho'ard]

Thanks for that. Smart condition OK on all drives.

[IronMac]

Weeks? Months? Gee, at the first hint of trouble...I'd be doing backing up and pulling the HD out! I had a drive that took about two weeks to die...

[ho'ard]

I have 4 drives n the MDD and one external, and have reasonable back-ups, so it wouldn't be the end of the world if I lost one. ut I do want to get a big drive to back up everything to.

[MacMagus]

> What causes the clacking? It's like a clack-clack, clack-clack, clack clack . . .

Usually it's read/write heads engaging/disengaging or calibrating. Some drives are naturally loud, particularly before they've warmed up after a cold start. Seagate drives are notorious for making loud clacking noises during thermal calibration, which can happen often enough and loud enough to drive otherwise quite stable personalities stark raving mad.

If a drive SUDDENLY starts making clacking noises with no previous history of being noisy then it's a good sign that there's trouble ahead. Make sure your backups are up to date.

[ho'ard]

Clacking still completely gone after a few hours of use and several restarts.