Last weekend I decided to change out the 0w40 Mobil 1 to GC 0w30. I understand that GC is suppose to be protecting better, but the infamous LS1 piston slap is louder now with GC. In fact, even after the car is up to temperature you can still hear the tapping sounds...especially around 1700 rpm when the engine is revved up and the RPMs settle back to throttle around. I may be overreacting, but I am little concerned that there is so much more clatter now with the GC. Should I consider switching to something like Amsoil 5w40 European oil?