My engine started going clan clang clang..... this morining and then just shut off. What is wrong with it? Freshly rebuilt with less than 500 miles on it? Any ideas? 289. Do you think its detonation? The builder said it had 11:1 comp but he said to run it on premium and it will be fine? It was offly loud as i cold hear it in the room that was next to the driveway where the car was sittin. ANY ideas?