2004 Acura TL reverse noise and vibration

Hey guys I have a 2004 acura tl with a little over 60,000 miles. The problem is whenever I put the car from neutral to reverse I hear a sound "gump" and feel a small jerk and sometime when the car changes gear when driving I feel a very small jerk. I changed the front and the left side engine mount, the rest seems good. But stilll get that sound. I tolfd my mecahnic about it and he said it he is not sure hwta it might be. But its nothing to worry about. Well I am. I would to know the possibilities. Hope its not the tranny