My guess is that its the poor design of the rear subframe mounts. Many are replacing them with M3 subframe bushings, and the difference is day and night. Gone is the squat and wallowing feel, transformed into a very solid, planted rear end. In my opinion ride quality is enhanced, not degraded. Check out HP Autowerkes for the mounts, they also rent a removal/installation tool which is well worth it. I tried doing the McIver thing and create my own with limited success, and much frustration. That should fix your rear end complaint.