Yeah.. it's probobly the read/write arm hitting the side of the platters... usually happens when a HD is about to die... do what grav said and backup fast...
Yes. Buy a new one. Unless you want to destroy it by opening it up and trying to reset the platters. Then no.
Over time the platters get offset. The clicking could be the platters hitting eachother or the arm hitting them. Either way. Nothing you can do about it. Go buy a new one and back up asap.
Well, after you back up, it can be(usually) sent back to the manufacturer to be refurbished. But that may not b worth it.
"why I've gotta be one of the cool kids just to walk by/
- without being tripped, thrown down on the ground and kicked/
Insulting me for no reason, I was treated like shit/
The teachers let it happen/
I've even seen some of them teachers laughing/
That's why I had a smile on my face when I started blastin/" - Ill Bill - The Anatomy of a School Shooting