I have a 1995 Buick Ragal and I hear a rattle in rear of car and when I turn a corner or go over a bump it makes a loud thump.
This happens to a lot of people. Perhaps your spare tire is not fastened down correctly. Other simple causes is your exhaust moving around due to it rusting through.
Check the rear sway bar mounts, if the rubber is shot you will get noise
Search Buick Regal Questions
Buick Regal Experts