Loose tailpipe (broken hanger or bracket), EDIT It could be the Exhaust system, as mentioned above. However, more likely, its the rear suspension. Rear struts, strut bearing plate, spring, or something along those lines. I suggest taking it to a muffler shop, and asking them to do a free inspection on it. Then you can determine if its something you want to tackle on your own, or pay someone else to do it.
probably your rearend
Probably the U-joints.
CHECK THE EXHAUST.MINE WAS HITTING THE BODY AT BOTTOM OF REAR FENDER
You probably need your bearings repacked
Im not 100% sure. but i have a 97 Monte Carlo. and i think i have isolated the sound to the gas tank expanding and contracting. it has a plastic gas tank, and the sound sounds similar to a plastic drum/barrel/container clunking from expanding/contracting.
It is most likely one of three things... 1 broken strut spring 2 worn out sway bar bushing 3 loose muffler
the rear end (differental)
The wheel bearing
What type of noise? Clunking, squeaking, rubbing. A little more information would help.
When your rear trailing arm (rear control arm) are bad you will hear a clunking noise when going over bumps and potholes .... This noise is louder and more noticible while you have passengers in the rear seats..... You will also hear your tires squeek a little on turns
Check you E-Stop Brake on the rear.
For a start. It has to do with the rear suspension in the struts. GM greased them for me but that did'nt last. They need to be replaced and that can be costly, so I just live with it.Hope this helps ....Ken