crfeaks and groans from hitch area

Just bought a new caravan, heavier than the first one but still light and well within cars capabilities ( Eriba Troll). Whislt towing home started to notice that on bends or steeply cambered roads and slow speeds  there was a lot of groaning coming from the rear of the car / hitch areas. Wasn't there with the lighter van. Any views or suggestions welcome. Thanks