So I replaced the HDD in my MBP yesterday and everything works fine. Took out the stock 120 GB HDD and put in a 320. Like I said, everything works fine. But (yes, there's a but) now my HDD makes what can only be described as a "purring" sound. It doesn't make it all the time, but enough to bother me. I'm not sure if I overtightened or undertightened some screws but since this noise wasn't occurring before, it's obviously a result of my "handiwork". My laptop is out of AppleCare and even if it wasn't, I think my HDD replacement would have voided it anyway? Thoughs or ideas? I guess I could always put my old HDD back.