To start this off i have an 04 WRX and it is totally stock. When the car is in neutral and i rev it i started to hear a rattle sound when the rpms dropped back down to about 2200 rpm. The noise is not there during acceleration but only during deceleration when the rpms drop. I popped the hood and had someone rev it for me. It sounds like the noise is coming from the turbo. I know the turbo heat shield comes loose sometimes so i checked it out and it seemed tight. What are some other things that i should be looking for? Is my turbo possibly on its way out and should i bring the car to the dealership and have them take care of it?