clicking sound

i hear a clicking sound when I change gears. Yes I am afraid it is an automatic, but hey I am very happy with my new toy! Nonetheless, the sound seems to be getting louder and more often. Just bought the car in May so it's under warranty but my mechanic said because I drive my car so hard(ya right! ) it probably won't be covered. He gave me some story about the manufactures being able to tell if the car has been driven hard.( Sorry, I just can't help but go just a wee bit faster then those little Honda's on the freeway. Especially when they challenge me. Just doesn't feel right letting them pass me up.) Anyway the noise only happens when I shift gears and it is more prevalent when I go from Park to another gear. I do not hear it while driving or going over a bump. Has anyone experienced this ?

miles are at 36,000 bought it with 20,000 on it.

thanks!