Suspension Noise problems of the 2007 Buick Terraza

I have had nothing but trouble from the start with our car's stability system. The back end was making a terrible thumping and grinding sound every time I would go over the slightest uneven surfaces. There have been multiple repairs made including replacing right rear bushing, rewelding of an unknown part on the right rear and the stabiltity/abs systems repaired multiple times. Yet, the car continues to have suspension problems. It has a unstable, wobbly ride especially on the interstate. Among other things I've also had a wheel senor replaced. We bought a Buick Terraza conversion van and have come to find out that they have a problem with the rear end that affects the stability of the car. I called braun mobility about a recall for the suspension problems and informed them of the multiple repairs. Superior mobility inspected the car again and has been my ongoing contact for problems with the car. They referred me to beck auto service who has done must of the repairs. Early on, shortly after we purchased the car, there was some sort of wiring problem that caused the "check engine" light to continually come on which was repaired by andy mohr gm dealer. To add insult to injury, I've had trouble lately with the van not wanting to start because the key won't turn in the ignition. In addition, we've had ongoing problems with the automatic doors malfunctioning; both power doors on the vehicle have failed to close on several occasions. The power door on the driver's side ocassionally requires multiple attempts to close and often the door warning chimes will not go off, even when the door is closed. I am still having suspension problems and would like to have a solution that works. This vehicle is used to transport my diabled husband and the ongoing problems have been extremely frustrating. The car is a 2007 Buick Terraza with less than 44,000 miles!!!.