2009 Other Toyota Models Noise in the transmission

I just bought a brandnew Toyota Venza V6 5 months ago. It was running smooth until about 2 months ago I noticed a "Click" sound underneath whenever I start my car running. I noticed the sound whenever the gear shifts from 1st to 2nd more when the car is "cool" or parked for a long time. I just hear it once and then you wont hear it when the car runs already. I took it to the Toyota Dealer Service center where I bought the car. They checked it. THe mechanic test drove and heard it. He said it has something to do with the "fluid in the transmission" but nothing to worry about. He also said he tried different cars there and noticed the same to some cars. Now I noticed the sound more frequently. Frequent in the sense that even if the car is not "cool" or not parked for a long time, as soon as I start the car running, the first gear shift from 1st to 2nd I hear the "click". What it this? Im worried it gets worse. The sound is like something got loose. What will toyota do to this problem?