7200rpm SATA disk (custom config when ordered uMBP) keeps stalling (beach ball) every so often Hi, i used Disk Utility on my uMBP and it was corrupted so i repaired it and my system still hangs every 15-20 minutes. it does this no matter if i'm launching an app or just doing nothing. so i formatted my drive and reinstalled OSX Snow Leopard. It seemed fine but now it's doing it again. Using Disk Utility shows nothing wrong with the drive this time. Is anyone else experiencing this? I'm still under warranty but I don't want the downtime of taking this in.