Unibody (Late-2008) MacBooks have a relatively audible hum

Owners of the new unibody MacBook Pro computers have noticed an audible hum that can be heard in silent conditions.

Apple Discussions poster doctorholliday writes:

"Yesterday, when returning to my desk, I realised that my MBP was making a humming noise. It is not super loud and if I had bad hearing, I probably wouldn't notice it. So instead of being super quiet and the occasional clicking of the hard drive, I have a continuous low level humming noise."

Some users have been able to muffle the sound a bit by pressing slightly on the casing of the computer, which indicates that this a mechanical problem. As such, it appears the computers may need some extra dampening to help with the noise, but it seems this does not hurt the computers at all and may just be from a "settling--in" of the components.

For other users, however, this problem materialized after applying the recent firmware update for addressing trackpad issues with the new MacBooks. Therefore, in addition to components breaking in, another potential cause includes errors in the new code for interacting with various hardware components of the computers, such as mishandling of voltages that could stress components.

For some users, the various noises developing over time and then disappearing after a few days, so it is recommended to monitor the sounds and allow the computer to break in a little. If the sounds get worse then it is recommended to take the computer in for servicing; however, most likely Apple will not cover mild humming sounds if the computer is otherwise functioning fine.

Currently the recommendation for affected users is to trying the computer on various surfaces to see if one helps dampen the sound a bit more. Beyond that, resetting various hardware components might have a remote chance of fixing the problem. Things users can try are resetting the PRAM and the System Management controller.

Things to try

Reset the PRAM Reboot the computer and immediately after the boot chimes, hold down the options-command-P-R keys all at once. Hold them until the computer resets and makes the boot chimes three times, then release the keys and allow the computer to boot normally.

Reset the SMC Shutdown the computer and remove the battery and power adaptor. Then hold down the power button for 10-15 seconds to reset the controller. Plug the battery and power back in, and start the computer back up.

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