Transmission Gear Slipping problems of the 2009 Hyundai Elantra

2009 Hyundai Elantra brand new bought. 1. When the car is put on 'parking' on a hill, it slips back about couple of feet. It seem like gears were not working properly (not in position) because I felt and heard clicking noise that sounded like gears slipping by not being in correct position. 2. It doesn't happen all the time but quite often when it's parked on a hill. About 1-2 times a week. When it happens and I try to see if it repeats, by going back and forth the car and put on parking again, it does not seem to repeat. 3. I haven't done anything to fix the problem because it works after the slippage. But I am thinking to take it to the dealer as in worry of further transmission failure. Only concern is that because it doesn't happen all the time, not sure if dealer will be able to fix it because they usually don't care unless they see them with their own eyes.