Mine started clicking too, so I ran the disk utility, no problems found, ran the hardware test, no problems found, used Seagate's online testing facility under XP, problem found, then went back to OS X, hard drive failed S.M.A.R.T verification. Phoned Apple support, told me if it passes the hardware test it's fine, even though it's showing as failed in the disk utility. It passed the hardware test but was still saying failed in the disk utility. Thought a full reinstall of OS X might help, tried it and now it says it's fine, no S.M.A.R.T problems🙄 😕