Any Ideas

Ok, last night I picked up a 98' SE with the 2.4l and automatic trans. It has about 151,000 miles on it. I drove it down the road and it drives out good, motor is tight and the trans shifts good. I did notice one thing when I drove the car. At highway speeds if you decelerate and then accelerate(like if you are just slowing down,coasting) you can feel a really brief shudder, really more like a light thud. The car drives fine other than that. I picked up the car at about 11 o'clock last night so I really haven't had any time to look it over. It was a free car so I really didnt ask many questions, my parents bought it and asked if I wanted it so I said yes and left it at that. For the short amount of time that I drove it I thought it may be a motor mount.