Brake noise can most likely be caused by the following issues;
Disc Brake Hardware-Caliper bolts, sleeves bushings and clips. These must be new or in like new condition. Caliper bolts, must not be bent and must be torqued to manufacturers specifications. Caliper slides and bushings must be clean and lubricated with the manufacturers recommended brake caliper lubricant. Clips hold pads in caliper should be replaced with new ones during every brake job. You must look up and use the recommended caliper lube procedure. All manufacturers have very specific lubrication procedures. This lube is there to prevent vibration-induced noise. Failure to follow these lube procedures will result in unwanted brake noise.
Rotors- Even new rotors should be treated to a non-directional finish. All manufacturers now recommend a non-directional finish on rotors. All rotors should be washed with soap and hot water before installation, solvent type cleaners do not remove all machining dust and drying with compressed air usually results in oil contamination of the friction material. It is also very important to make sure that the wheel flange behind the rotor is free of any rust or debris. This will cause rotor runout, which over time causes friction material to be transferred to the rotor surface. This will eventually cause noise due to extreme rotor thickness variance. It is also imperative to use an on car lathe when it is recommended by that cars manufacturer. Most all manufacturers feel it is the only way to turn the rotors on vehicles and not produce runout.
Pad fit in the anchor. Anchor brackets do wear out. The pad should fit very snug in the anchor bracket. The factory maximum clearance is only .010. Most squeal noise is caused by loose fitting pads in anchor bracket. Some OEM's have Bulletins hat explaining lubrication of pad retaining clip for this reason alone.
Proper pad break in is critical. Any time you perform a brake job, you should perform 30-50 moderate stops from speeds lower than 40 mph. There should be a minimum of seven tenths of a mile cool down between stops. Excessive heating or hard use when new will assure that your pads become glazed and will never break in properly. This break in procedure is outlined many owners manuals.
Proper lug nut torque. This cannot be stressed enough. Improper lug nut torque will cause rotor deflection. This deflection will (over time and 2-3k miles) cause RTV resulting in noise and brake pedal pulsation. This will not manifest itself until some mileage has accumulated on the vehicle causing you to believe that the noise is not related to the original brake job. Always use a calibrated torque wrench and look up the proper wheel torque for the vehicle you are working on.
Read the service procedure and all TBS's for the vehicle. Some calipers are small and prone to vibration. The manufacturers know this and have published a lot of information on how to prevent noise and vibration on these vehicles. Domestic manufacturers also have many revised brake service procedures that relate to noise prevention.Take the time to familiarize yourself with the proper service procedure for the vehicle you are working on.