On the inboard pad, there is a device (wear indicator) that when the pad gets to a certain thickness, comes in contact w/ the rotor, letting you know that it is time to change your brake pads. The inboard pad wears at a higher rate for some reason. The indicator is a small hook shaped piece of metal on the end (?) of the pad. If it isn't touching the rotor, then some anti squeal compound on the back of the pad may do the trick. Check out your manual (Chiltons/Haynes), it is all explained there.
John