Hey guys-

My girlfriend has an '01 626 with a horrible clunking sound coming from the rear every time the car hits a bump. I replaced both struts and strut mounts and the clunking was still there. When I started hitting things on the bottom of the car with my hand I discovered that the problem is a thin bar that goes from one wheel to the other, connected on each end by a sort of ball joint.

What is this? A rear stabilizer bar

 

Sure sounds like it to me!! Like all late model Mazdas, the rear has an independent suspension so the only thing going from one side to the other would be the sway bar.
Where... what part is the clunk coming from?
If it's the mounting bushings that are shot you might be able to find a poly set at your local parts store. Be able to convert metric to std though. 1"= 25.4mm. 7/8"= 21mm, etc...
If its the end links, you may have to go to the dealer, but I would check the online sources first to see what's out there. Ya' never know, y'know?

 

Well, I have the same car with the same problem. It comes from the rear sway bar with a crack ball joint. Once I replace them, the noise is gone.