Even new pads can squeak and cause a headache. The sound comes from the the pads vibrating against the rotor at a certain frequency - like all sound, just not as pretty as a piano or guitar (or pan flute if that's your bag) :) That's why people often get new or worse sounds after installing new pads. It's just a situation of a new vibration creating a new frequency. I have even had it happen after removing the wheel and reinstalling it, without changing anything but an inner tube.
There have been many options for trying to control this issue - "special grease" that goes behind the brake pad, and EBC will even send you a free pack of "damnpening pads" that you install with new brake pads. They don't advertise it - but once I heard about it, a simple email request had them on their way from EBC, no charge.
The bottom line is all or none of these things may work. Or, you could remove the pads/wheel/caliper (one or all), reinstall them without changing or adding a thing, and have no sound at all.
Kawasaki Versys**CL360 Project**Honda CB 550**Husky TE610**'72 XL250 for the lady
-- a blog about wrenching on bikes in Barre, VT...