Always always always do a visual inspection of your pad wear when dealing with odd noises. If pads wear funny, they can definitely sound funny. When doing a visual inspection, make sure you check top bottom and middle of both the inside and outside pad. To be safe if I'm concerned about it, I'll pull them right out and inspect them.
If you do pull them out and find them glazed over pretty bad, that will cause some odd noises when braking. You can skuff them up with some low grit sand paper and that usually clears that up. You can also sand down the hard edges too if you want it to be quieter (take the 90 degree edges and make them small 45's instead).
Try lubricating the edges that the pads slide on with some silicone brake lube so they move back and forth in the caliper a little more freely.
Inspect your calipers and master cylinder for a fluid leak. If you are low on fluid, it's coming out somewhere or your pads are worn low. I don't know exactly what happens if brake fluid gets on the pads, but it's not good for them, not to mention you're probably spraying this stuff off your spinning rotor/wheel and will end up wrecking the paint in the surrounding areas.
