I've noticed that usually when I first run the car it runs smooth and the engine has a pleasant low growl. After about 10 minutes of driving it a bit hard, it becomes increasingly noisy and sounds like the engine is having a tougher time, rather than the smooth low engine sound. Anyone know why?

 

Is it idling a little higher after 10 minutes? Not sure if this is your problem, but I experienced the same thing where it would sound pretty rough and I noticed it was idling a tick higher than usual. It turned out to be the surging issue covered in one of the TSB's. The dealership reflashed the ECU and the problem went away.

 

OP... see my thread and if this is what you are hearing then the instructions to have it corrected are posted...

https://www.myg37.com/forums/engine-...dentified.html