in first gear the transmission is multiplying engine speed through the front and rear gear sets.in this mode the reaction members of both gear sets are in reduction therefore the input speed is faster than output in both gear sets creating noises which are caused by the ratio and biasing in the gear set.the rotating speed in reduction of both sets generates noise.now on a 1/2 ratio change the rear gear set becomes dead and the front sun gear is divided into the ring gear which reduces reduction and as a result generates less operating noise than in first gear.the trained ear can listen to and understand the acceptable noise produced by a planetary gear set.also if your interested in studying planetary gear mathematics go to industrial press.com and order the planetary gear master handbook volumes 1 thru 3.some noises in reduction may be a sign of worn components,but very few things in this world light a bulb in my mind like the sounds of ratio changes in an automatic combined with my unique understanding of their principles of operation.
