The clinking and clunks of the hards when it spins it not always the desired problem, The drive itself does fuction but in a serverly limited capacity. But as each time does by, each new scrape, pit and dip in the platters represents new and hard problems. When in a raid enviroment, how it is configured and how the controller monitors them with the software as well, makes it hard to diagonse it. True raid controllers show you if an error exist in your configureation. As the other have mentioned above, i would recommend you to investigate further.