Brake Noise

[higguns]

So i just bought my mazda 3 about a month ago and since i got it the front brakes started making noise as i was driving (not even applying the brakes), like a pulsing noise that increases with speed. its like the brake are dragging. so i take it back to the dealership where i bought it and the dealer drives the car with me in it and of course the noise isn't there. so i drive it home still no noise. i go to drive to class later and the noise is back. so i bring it to his mechanic and theres no noise when he drives it. right when were bring the car back into the parking lot of his shop the noise starts. he puts it on the hoist and looks at it. he shows me a spot on the rotor where apparently theres a buildup of rust from the car sitting on the lot at mazda. the pad touches the rust buildup and makes noise.he tells me the pad will wear down in that spot and the sound will go away.
thinking about it after, the pad will just wear down in that spot and then when the rest of the pad wears down it will touch again. so i was wondering how i should go about removing this buildup. pics below kinda show the buildup.
http://img188.imageshack.us/img188/8686/28092009073p.jpg

i had the car check at mazda before i bought it and they said the brakes had just been done recently, so i dont want to replace anything if i don't have to.