Thanks for the info. Make sense now. Maybe in my wife's F25 X3 but not in my E92 '07 M3. But then again for what it cost I don't know whether it's worth.
2007 E92 6MT - Silverstone II with /// Performance Exhaust with ACM Test Pipes and BPM Sport Stage II Dev-Tune
2011 F25 X3 3.0d