Why does my Mac sound like rebooting without the chime?
After I boot-up or reboot my A1150, it keeps on making the reboot sound without the chime, i.e. the whirring/grinding noise. If I run my defrag programme it disappears. Very tedious!
Depending on the age of your HD it may be failing or getting ready to fail. Keep a current backup, and check the SMART status of the drive.
Running Apple Hardware test may also provide some information.
Some anti-virus, or backup software can also cause a lot of drive reading/writing. Applications->Utilities->Activity Monitor may be able to identify which App is being active.
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