I just upgraded my 13" Macbook Pro 2.53GHz Mid 2009 to the Momentus XT 500Gb and its pretty quiet, but not practically silent like the original Hitachi 250Gb drive. It sounds like a little fan is going pretty much all the time. I also tried the Western Digital Scorpio Black and it wasn't much quieter. -------------- Are there any almost silent (fast would be nice) drives other with 320Gb+ other than SSD? Might there be a hard drive controller or something Apple loads onto their factory drives that makes them quieter?