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I have a Macbook Pro and it makes that crackling sound at least once a day for a while and then goes away. I hope that it's not bad.

mine makes it whenever i open an application, whenever the HD works i have a Seagate Barracuda ST3500630AS HD in my iMac, my old PC used a Maxtor HD, it makes a LOUD crackling sound hearable from over 5 yards away EVEN if its in its wooden box thats built into my desk!!
 
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