The day I bought my Macbook Pro 13" 2.53GHz I replaced the HDD to Seagate Momentus 7200.4 500GB, but since then I face lagging while watching videos or even doing anything, I hear the HDD clicking and lagging for a second (I guess its compatibility issue with the HDD!! or Maybe Mac OSX is buggy?). Im planning to replace it with a better one. What do you advise guys!!