My MacBook is a little more than three years old, and I just recently had to replace the hard drive. My new problem is that the computer makes a whirring noise all the time. It rarely happens when I am using the computer. But if it is on and just sitting there, it makes a starting up, whirring noise every 30 seconds or so. Also, if I put my computer to sleep, if will frequently "wake" back up. The screen goes black like it's asleep, and then two minutes later, it's awake again. The only way to get it to stop making noise is to turn it off. Is something wrong? Is there some way I can fix this?