I had a similar thump in my '90 that I ended up fixing by replacing the bushings on the trailing arms. Mine were still original so I guess that after 20+ years they were gone. My noise was:

-low speed thump, especially when stopping/re-accelerating or going around corners at low speed (e.g. in a parking lot)

-more pronounced/obvious when it was cooler outside, like once the fall morning temperatures were down in the 60s

-in my case, you could feel the 'thump' through the floor with your feet

Not sure that it would be the same thing, but it drove me crazy until someone here suggested that it might be those bushings. Once I replaced them it went away.

steve