Hi, this started about 3 months before i got the head gaskets replaced, now that they are replaced i still hear the knock, especially in the cold when i start the car. i want to get this taken care of asap! i have a 90 sc that just turned over 87,000 miles. what is this knocking, and will it hurt the engine if i drive it the way it is. i have never EVER used any octane less than 93, and i have been even using 94 in it every once in a while. Help please i dont know how much longer i can go with the engine sounding like a dump truck!!!!!feel free to instant message me when i am online (ThunderSC300) is my S/N. thanks, brian