My 98 SE has the clunky noise from rear bottom. It happens when I drive over uneven roads or hydro lids with the speed only at 30-40 km/h. The noise can be heard clearly when I drive on highway when there is a solid wall on my left side.
Once I punch on all the tires I found on my rear left tire there is a vibration noise. But if I pull up the hand brake, and punch the tire again, there is no noise. I brought my car to a shop and they have it checked. I was told the springs in the rear wheel(drum brake) have lose tension. But they have the springs adjusted. Now the situation of the noise has improved a lot. But I will have all the rear wheels' hardware(springs) replaced this weekend.
HTH
Erwin