My iMac wakes up from sleep at random times. The screen doesn't come on, but you hear that kind of mechanical sound the computer makes when you press the power button to turn it on or when you wake it up from sleep, and you hear the hard drive start to spin for about 3 seconds, then it goes off. It's so strange and sometimes it even startles me. It's only been doing it for 2 months and only does it when I put the computer to sleep. Is this a fixable problem, or should I take it in to the Apple Store and have it swapped out?