I parked the Z at a friends and left. While I was away, I was told that the car made really loud noises like water boiling, rattling for about ten minutes. When I came back and was told of this I turned the key on and I could hear the sound of like a power transformer before turning on the engine. When I turned on the car, all was normal, but when pressing on the accelerator there was a sound like the car was backfireing.