Mac notebooks: Noise when powering on or waking from sleep is normal
When powering on or waking from sleep, some components in your notebook may make unfamiliar noises.
For instance, when optical (even if there is no disc inserted) and hard drives first receive power and make themselves ready for use a whirring or buzzing sound may be present for a few seconds. Additionally, fans in the computer may start off at full speed, but will taper off as the computer continues to start up or finish waking from sleep
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