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When I leave my MacBook Pro 13" level for a minute or two (sometimes I only need to keep it level for a few seconds), and then pick it up and turn it on it's horizontal axis, I hear a single click, coming from either the hard drive or the Super Drive.

Is the click I am hearing some sort of locking mechanism in the hard drive? Or in the Super Drive?.. And therefore nothing to worry about. Or is either my Super Drive or hard drive faulty?

Here's some System Profiler info about the hardware:

Revision: HC10
Serial Number: UK30 1602WH
Native Command Queuing: No
Detachable Drive: No
Power Off: Yes
Async Notification: No

Hitachi HTS545025B9SA02
Capacity: 250,06 GB (250.059.350.016 bytes)
Model: Hitachi HTS545025B9SA02
Revision: PB2AC60W
Serial Number: 100326PBL2003SHDB87V
Native Command Queuing: Yes
Queue Depth: 32
Removable Media: No
Detachable Drive: No
BSD Name: disk0
Rotational Rate: 5400
Medium Type: Rotational
Partition Map Type: GPT (GUID Partition Table)
S.M.A.R.T. status: Verified

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There is a rule. You shouldn't change the direction of a hard drive from vertical to horizontal if its been running in one way already for a while. The clicking sound in my opinion the stopping of your hard drive. (At a laptop it means you shouldn't swing it around while it's running. Suspend it if you want to move fast. If not, then just move it without sudden movement, etc.) (Don't know about MACs but ThinkPads have a speed-o-meter and if you move it like that, you will hear a clicking sound and the HDD stops to prevent damage.)

Not faulty at all I guess, but yeah you can kill your hdd if with this.

(After a search on Google, yeah Apple uses a similar technology like Lenovo/IBM does, the HDD stops to prevent/minimize the damage.)

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It's a laptop. Saying "Don't move it if it's on" is pointless. It's inevitably going to be moved, and will have been designed to take that into consideration. – Fake Name May 16 '10 at 14:18
Maybe they SHOULD but it's definitely not the case. (Nowadays laptops are only protected from this. (Only Lenovo and Apple applies this way though.) Basically its against dropping down and such. When the meter hits the limit, hdd stops, so even if the laptop breaks into pieces, you may be able to get your data back without a problem.) Moving your laptop while its on is reducing the HDD's lifetime , really much. Basic lesson/advice for every laptop user/owner. (Okay if you move it carefully like you can't even see on the sensor application, thats not a problem. – Shiki May 16 '10 at 14:21
up vote 1 down vote accepted

I called Apple support. The customer support agent told me that the sound I was hearing, is the hard drive read/write arms locking, to prevent them from physically damaging the magnetic plates inside the drive.

My MacBook Pro is equipped with an accelerometer, which triggers this safeguard.

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Lol just what I wrote. Ehh. FACEPALM. :)) – Shiki May 19 '10 at 21:42
It's called the Sudden Motion Sensor (SMS). – bwDraco Nov 10 '13 at 3:24

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