I have an external hard drive connected to macbook. When I am listening to music and my mac is not in sleeping mode everything is fine, but after 15 min. when display is turning off and music is still playing my hard drive has very weird behavior - it looks like it turning on/off every 40 seconds 'to load a little bit of music and continue sleeping' making simultaneously ugly sounds/snaps. I don't remember the same behavior when I used Windows.
It's likely just the parking of heads and the disk wanting to stay in "sleep" mode. You can read more about that here.
One way to stop the disk from going to sleep (some external enclosures have extreme disk sleep settings to conserve power) is to use pmset.
For example, to prevent an attached disk from going to sleep while your device is plugged in to AC (charger) is as follows:
It's of note that this prevents all disks from going to sleep, not just the external enclosure.
pmset is the program that handles all power management settings on OS X. The Power Management Preference Pane is just a front end to that utility. All settings are persistent (saved on reboot) and are actually written to a plist (
Additionally, you could try using HDAPM (I ran this for months before I moved to an SSD).
I would suggest trying to use pmset to prevent the disk from sleeping. It works on most external enclosures, but if you find that it's not honored by your manufacturer, you may have to find an alternate method. I've found WD and some Seagate enclosures to be problematic. pmset is not a hack and should be honored by all device manufacturers; however if you find that yours is not, try heading over to their support forums. They may have a firmware update or more information.
Lastly, if you suspect the drive of premature failure, you'll have to run a proper analysis of the drive's physical health. Disk Utility is not a reliable program in this case, as it deals with filesystem structure and integrity. You will want to use either a 3rd party utility (like Disk Warrior) or better yet, the free tools supplied by the hard drive's manufacturer (which will most likely require Windows).
You may have a drive hardware problem. If you are new to macs, you may have a drive that is formatted for Windows, and this possibly could also cause the noise.
To make sure that your drive is ok, you use Disk Utility. It's in the Utilities Folder, that is a sub-folder of Applications.
Run Disk Utility, select your drive, and then Verify Drive. It should not take too long. If it does turn out you have a problem, you need to get your information off of that drive asap. Then you reformat that drive (again, using Disk Utility). Then finally, check the drive once again.