I've done a search for this topic and opinions vary. Has anyone tried multiple 5400rpm HD's in their unibody macbook pro 15''? I have the 320GB 5400rpm Hitachi drive in mine. It is extremely quiet, but I can still hear the high pitched whirring of the platters in a mostly quiet room. I know this is normal, but the Hitachi just sounds too loud for my tastes. This is mostly to do with the thin piece of aluminum between the right palm rest and the inside of the macbook pro. So, who here has switched from the Hitachi to another brand HD (preferably 500GB and 5400rpm) and has noticed a significant reduction in whirring noise in quiet environments? I'm thinking about trying the WD Scorpio Blue and the Samsung Spinpoint in my macbook pro as a test. I'm willing to bet that these drives idle at different decibel levels. The Hitachi drive is very quiet, but the spinning of the platters makes a slightly high pitched noise that's grating for someone with sensitive hearing. I've confirmed this by running my mbp without the hard drive. Please share your experiences with replacing a Hitachi 5400 with another brand 5400rpm drive.