Thanks for all the responses. The issue (as always) turned out to be very simple - it was the cable, I was probably using a cable from an old cell phone, and with a different mini-usb cable it worked.
It's a little odd that the cable worked with a PC desktop, as it must have provided just enough power, but the Macbook couldn't give it enough juice and caused the click.
I hope I didn't cause any damage to the drive- on that note, has anyone used WD's RMA program? Is it worth doing this to get a new drive?