Unfortunatly, Nissan has the worst sounding tranny of all time I think. This thing is going to make all kinds of noises and for the most part are "normal".
Bring the car to the dealer just to have it on record for future references. If any mechanic laughs make sure you call him on it. In front of other people would be a good idea.
OP make sure you call the dealership on monday, even if you know he won't be there. Then you can mention to the service manager how you felt when he laughed at you / made you feel by asking about the problem.
