If that's a rapid clicking or buzzing noise that lasts about one second, you have a problem when it doesn't do that. Older transmissions used an accumulator to soften the engagement into gear for comfort. That was a spring-loaded chamber that had to slowly fill with transmission fluid before one of the clutch packs would apply. Your transmission is computer-controlled and doesn't use an accumulator. The valves are controlled by electric solenoids. If one were to turn on, you would feel a harsh, solid bang into gear. Instead, the computer cycles it on and off rapidly to vary the average pressure and rate the clutch pack applies. That eliminates the pounding when it goes into gear.
That's called pulse-width modulation. By varying the on-time to the off-time, they can vary the average pressure. The same thing is done when the other clutch packs apply for the other gears but you won't hear that. You may hear that ratcheting sound when it downshifts to first gear as you come to a stop. That is also done for comfort.
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Thursday, February 28th, 2013 AT 9:29 AM