When any braking system is operated, vibrations occur. However, should theses vibrations match the resonant frequency of another component of the system a magnification of the level of vibration results. If the sound level of this process exceeds about 60 decibels the resultant noise can be heard, at the low end of the scales as ”groan” and the high end as “squeal”.

Although the origin of all brake noise is at the interface of the pad and the disc during braking, the point at which this noise is ‘released’ is invariably between the backing plate of the pad and the calliper. Hence it is in this area that most anti-noise research has been concentrated, though centrally slotted and/or chamfered friction material also assists in noise dissipation.

Both Original Equipment and Aftermarket brake manufacturers have concluded that the most effective method of reducing the problem of brake noise is the use of a rubber coated metal shim affixed to the backing plate of the brake pad. Independent tests have shown such a combination to be significantly more successful than the, much cheaper but often-used, method of painting the pad backing plate with rubberised or “gel-like” materials. The effectiveness of these materials is reduced or often eliminated during the first session of heavy-braking.