Hardware :: WD MyBook Making Consistent Ticking Noise

This isn't strictly a Mac question, but I know there's a lot of knowledgeable users here and I'm sure some have the MyBooks too. I'm in the middle of the daunting process of reformatting my two 500GB MyBook hard drives (the standard black ones) to a Mac friendly format having been a Windows user for a while... having such a large HD on the iMac makes it not too painful, thankfully. However, I've got one of my drives hooked up at the moment, copying away. It's making a consistent ticking noise as it works.

It's been a while since I asked very much of my drives (generally I just read off them file by file as it were; playing video), so is this noise normal, or is this drive on its way out do you think? As I say, it is a consistent ticking, like the ticking of a clock really rather than scary whirring-clunk noises, and there's no trouble copying files onto my iMac at the moment. I just don't want to copy stuff back over if it's going to die on me. I've got a stack of DVDs here anyway and I think it's about time I updated my DVD copies of my files...