I have the exact same problem. The engine "grinds" - I have not been able to identify exactly when it occurs, nor the RPM, but it clearly happens. Almost like the turbo chargers are misfiring.
I also have a related problem (at least I think it's related). The engine will, from time to time, make a cackling noise, and act as if it's going to stall. Again, I'm thinking this is a turbo charger issue. Or perhaps fuel injectors, or an issue with the fuel pump. This problem initially occurred rarely, and now occurs several times per week. It's a real concern as it appears there may be a major design flaw in the transmission of this engine.
We currently have our car in the shop (in knoxville, tn), and hopefully I will have some more information to report soon.
