Very weird. Taking out the unit does void the warranty. How long have you had it? Youve tried shutting down the computer and placing the passport in another usb port right?
Look at this
http://jasontomczak.com/2008/05/26/western-digital-my-passport-elite-320gb-great-for-macbook-pro/
If your thinking of taking it apart. Anything else you might add that possibly can give me more details, please re-post
