I had that rear trailing arm bend in half on me. Dealer did not cover under warranty due to the Eibach springs. They could not explain what would have caused it. Mine was bent in half like a V when it happened. Luckily I was on a crowded City road and not on a freeway when it happened. It just felt like the back end wanted to break loose all of a sudden.
09 E90 M3 - Interlagos Blue / Black Novillo / Sycamore Anthracite / Eibach / HRE