Klunking sound from rear of car

I have a 1997 Ford T-Bird 128,000 miles. While driving I hear a klunking sound from the rear of the car. It happens at different times. I can get the car to do it while slowing down to about 30 mph and then accerating it starts the klunking sound then stops. I have also heard the sound while driving on the highway going about 65. I notice the noise while going around a slight curve in the road. Can you help. I don't want a tire to come off the car!