Noise has been an annoyance since man began to use friction as an engineering tool. With the advent of lubricated friction devices, many believed that noise would disappear. However, noise in ail-immersed (or “wet”) friction couples continues to be a constant and difficult problem for designers of clutches, brakes, and other frictional devices. While prediction of fractional noise remains difficult, understanding basic hydrodynamic factors that lead to noise can provide insight into this phenomenon. Factors that affect the hydrodynamic state within the friction couple, such as torque, speed, geometery, lubricant, friction material, and temperature, must be understood and controlled to eliminate noise and vibration in these couples. Field and lab experience may be used to provide empirical guidelines for control and prevention of noise and vibration in wet friction couples.