Bought my ST last August. At 4000 miles, the exhaust began to rattle and vibrate horribly when the engine decelerated through 1500RPM. Took the vehicle in and they replaced the pipe section which contained a mesh covered spacer. Noise stopped. But...at 10000 miles it started again. Bought vehicle back. They said it is turbocharger back pressure, but this time said it was normal and refused to change any pipe. Now at 11,500, it is horribly loud, and is frustrating and maddening. Most likely a design flaw. Has anyone else experienced this??