New disc pads take some time to bed down, even if you are using new or turned rotors and during this time when the pad is bedding in to match exactly the geometry of the rotor the pads can make noise.
The normal way to minimise this is to add
noise reduction shims onto the reverse side of the pads which dampens the vibration caused by the pad which will "Chatter" slightly when not seated perfectly.
This noise would go away after 300-500 miles but to avoid irritation
noise shims are used to reduce this sound.
There is no safety issue when a pad makes these
noises during bed in, it is merely a cosmetic problem of the new brakes.
At this point we also want to remind you that new brake pads do take some miles to bed down and that bed in times on worn or old rotors can be a lot longer and that DURING THIS
BED IN PERIOD BRAKES WILL BE LESS EFFICIENT especially if rotor condition is poor. If you are not sure what is acceptable and not, please ask a professional mechanic as driving a car with
poor brakes is just not a good idea at all.