i hear this strange rattle type sound coming from somewhere around the cams. it happens as soon as the car is started and stays the same no matter how hard I rev. My temp gauge has been reading near the H. so I pulled out the old Bosch +4s I had in there and put in NGK Iridium IXs. I also filled the radiator to brim with water and antifreeze. started it up and no change. I put the bosch spark plugs in about 4 months ago and they were mostly black with white at the tips. one had a little bit of oil around it. what could be the problem????