I have a USB2+Firewire external disk that made a clicking noise, and Mac OS X immediately unmounted it and put up a dialog box saying that a peripheral is misbehaving. The disk made a clicking noise several times in a short interval, and each time it did, the dialog box on screen would flash. So I unplugged it, waited for a few seconds, and plugged it in to another Mac, and this time it worked perfectly. I copied all 800 GB of data out of the drive over some 9 hours, and it worked perfectly and at its usual speed of 30 - 40 MB/second.

Now that all my data is out of the disk, I repaired the filesystem using Disk Utility. What else should I do? Should I run some kind of disk scan tool that checks the entire disk for bad blocks? Can you suggest a tool for the Mac? Since the disk has a HFS+ partition (and a FAT32 partition), I think I should run a disk repair tool on Mac rather than Linux. Is that correct?

I don't have SMART data since it's an external disk, and I don't want to break open the enclosure.



2 Answers 2


You covered step one well (backing up the data). Now, depending on the age, it sounds as though the drive may be failing. It may take minutes or months; a clicking generally indicates that the read/write magnetic sweeper arms (at least one of them anyway) inside the disk have suffered some mechanical damage and are dragging against the disk media itself. The clicking sounds arise as the arm moves away from the disk and back on.

You may also hear a dragging sound as the disk is spinning. As for switching computers and the sound going away I'm not sure of any causes. It could just be random, but it could also be a system software issue causing the disk to reset or act randomly (but this, I suspect, is doubtful).

If the disk is not very old it may just be a defect. I would check the disk's warranty, unless you've been hard on the disk by dropping it or moving it roughly as it was spinning; desktop drives, including external drives, don't like to move while spinning they are not designed quite like laptop drives are.

Well that's about all I can say, good luck with that.

  • Is it bad to even gently move a spinning external disk -- moving it very gently with no jerks at all? The disk is almost two years old btw. Thanks for your help. Feb 24, 2012 at 14:20
  • This is a 2.5 inch disk. It counts as a laptop drive, doesn't it? Feb 24, 2012 at 15:48

Seems to be an issue with USB power when connected to a macbook pro. Works fine when connected to three different desktops, and SMART data and an extended scan of the disk say that everything is good, so I am going to continue using the disk. Thanks.

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