As Ben said way too many variables to pin point it. If the noise is during a braking event it is more like likely a hard spot on in the pad/pads causing the high pitched squeals.
When braking for the fist time after the vehicle has sat over night, the high pitched squeal is the pads scrapping off (removing) the surface rust on the rotors. This drives my wife nuts and there is nothing that can be done to stop it.
To remove the hard spots on the pads Dave H M hit the nail on the head, get up to 40 MPH and when safe (a long empty parking lot is best!) apply the brakes with heavy force but not as to lock them up, three time. This will remove the hard spots and clean the rotors at the same time. Has worked for me every time.
Don