1999 Dodge Caravan Loud THUMP or BANG on acceleration

Just bought this vehicle, and visual inspection was good.

Upon driving a long distance, I had pulled over for a momemt to answer a phone call.

When driving back on the highway, a loud BANG was heard under the vehicle, almost to the center of the vehicle, and right of the drivers feet. I was only going 5 to 10 mph.

It was not as loud again, but did happen a few times during the long trip.

It seemed to happen when driving on a gear change climbing small hills too, but not as loud. I was going around 55 mph, and trying to get more speed.