I have a 2011 MBP 15" with an SSD in the main bay and HDD in an Optibay. It runs great but I've noticed that I hear the HDD once it "spins up". At first i thought it was the fan, but it's just the sound of the HDD. It's a Toshiba 7k750. Vibration and HD search/write noise isn't a prob. I'm wondering if switching the drive locations will help insulate that noise as I've never heard that noise before. Is the hard drive bay more insulated by chance? I can certainly experiment but I'm trying to minimize surgery at this point .