Galant 97 ES problem-thudding noise

I need an opinion (or opinions). I have had this car for 4 yrs now, bought it used and think it is an excellent car that has not given me any major problems. I always noticed a thudding sound when I would accelerate car after stopping 'specially on an incline. It happens occasionally and since I was living in the East coast then where most places where flat, it did not bother me much. Now that I live in NW where most places are hilly, I really notice it when I start climbing the hills and put my foot on gas pedal. I have tried adjusting my driving methods such as putting foot very lightly on accelerator to avoid the thud-sometimes it works, other times it does not , 'specially on steep hills. Is this a transmission problem? Or is this common among the Galant 97 cars? I looked around different forums to see if people had the same complaint about this car. Saw one complaint but was not very specific. It was a complaint about a thudding noise too and the dealer said that was how the transmission worked. I just don't want the car to end up with a more serious problem since I have been taking this for granted all these years. Thanks a lot. Any opinion would be highly valued!

I am new to the galant, 3 weeks now, and I have noticed the same noise.I normally drive in OD mode and the noise happens then. If I drive with OD off I don't get the noise.
Don't know if it's natural or not.

Thanks for the advice. I will try driving with OD off and see if that works.