My car sounds like it's going to break in the rear. What might this be?

The upper mount brackets on the rear strut assemblies (L/R) are famous for breaking. You can replace the bracket and damper to save money (price under $50 for each side), but the work is not for amateurs since the strut assembly has to be removed, the coil spring compressed, mount plate replaced and then the reverse before it can e reinstalled. If you are willing to do the work, save the money, because the alternative is replacing the whole strut assembly (about $200 for the pair if done yourself). Its easier to replace the whole assembly, but more costly. When shopping for the assembly, look for shock/strut "quick assembly".

rattle noise in under body of 2008 sebring convertible (48,000 miles).

My daughter has a 2001 convertible. The rear strut broke loose and sounded like the rear was going to fall out. The aluminum mount that holds the top of the strut at the body connection corroded from road salts and broke apart. Much rust on the undercarriage suspension and brakes, too. Had to replace the calipers, rotors, pads and all struts. Also, the rear ball joint just let go and she's in S. Carolina. I had her tow the car to a reputable repair shop that other family members had used. Waiting to hear the estimate. She got a good deal buying, but we put a lot of work into repairing it. http://www.rockauto.com/ is my go-to parts store!!