ok so i just swapped out my stock 250gb hd for a new western digital 750gb 7200rpm drive. It works fine, it boots up, and has all my files on it, but its really laggy. Its not a constant lag, but instead it will be completely fine for 5-10 minutes and then freeze for 1-2 minutes. It gets really bad especially when i watch a movie on itunes. This really doesn't make sense to me, I had been using it as an external drive in an enclosure for a few months prior to installing it, but i dont see how that could be an issue. It also seems to occasionally make a slight buzzing noise...any ideas?