It is impossible to see brake noise unless you have laser vibrometer. Two students from the Georgia Institute of Technology took a laser vibrometer and a corner of a car and answered the question of what is actually making noise during a brake squeal.
A laser Doppler vibrometer (LDV) is a scientific instrument that is used to make non-contact vibration measurements of a surface. The laser beam from the LDV is directed at the surface of interest, and the vibration amplitude and frequency are extracted from the Doppler shift of the laser beam frequency due to the motion of the surface. The output of an LDV is generally a continuous analog voltage that is directly proportional to the target velocity component along the direction of the laser beam.
The students built a webpage that can be understood by more than just engineers. Take some time to look at the laser vibrometer pictures, especially the ones of the caliper ears and abutment clips.
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