My sons truck was running fine. He had just changed the oil and checked all the fluids two days ago. When he was coming home from work yesterday it started whining and knocking, he drove a ways and the oil pressure dropped. It was full of oil and he checked to make sure the filter was properly installed. Think maybe the timing chain broke causing the knocking (did not change with rpm change) and maybe the oil pump quit or screen got stopped up. He got in it this morning and it run like a dream for about an hour and then it started the knocking again and the oil pressure dropped again. Any Ideas????