Either shims or disk brake quiet smeared or sprayed on the back of the pads. This goes for any disk brake car, its just that some are worse than others about the noise. The squeal is actually coming from the backside of the pad where it vibrates against the caliper piston.
There are several factors involved as to why you are hearing the squeal, which is more than likely pad vibration.
What brand of pads did you use?
Who did the work?
What steps were taken to eliminate pad vibration?
Was every surface the pads come in contact with on the caliper lubricated properly and with the proper lubricant?
Who turned the rotors?
Were they at or below minimum thickness?
Did they chuck them up on the lathe properly?
Were they washed before installation?
(Rotors should always be replaced with quality rotors that have an oe equivalent compound and cooling vane properties. Rotors are made much differently these days to reduce un-sprung weight and turning a rotor is not what it used to be.)
Was an initial break in period performed to give the two braking surfaces an opportunity to mate?
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