said by mmainprize:Maybe he clean the inside of the case with air and got dirt inside the drive. Or the drive got bumped and became out of alinement and is now making noise, maybe a few light taps on the desk will get it inline and it could stop making the noise.
HDDs are sealed devices and I've never heard of that seal opeing up on its own. However, cleaning case fans and filters could allow more noise to be transmitted to the outside especially if they were plugged up from gunk.
That still doesn't account for the fact that one drive is noisier than the other though. My experience is that when a drive changes in sound it also has a change in errors. Have you run any diags on it?