I just installed H&R lowered street springs in my 528e. I think the rear of the car is riding too low and harsh with the Boge Turbos I installed at the same time. I'm also getting a vibrating noise coming from the rear when the road is rough. Sounds like something resonanting noise due to the spring stiffness. Never heard the sound before I changed the springs...Can anyone comment on the Eibachs or perhaps if M5/535is springs will fit in the car and their ride quality?