I have F150 1999 model manufactured in 98. I got a oil change one day. I was driving about an hour later I hear this knocking sound. It sounds like it is coming from the top and bottom. The truck has less than 40,000 miles on it. Are the engines still bad? How can I tell if it is the same problem the 97' engines are/were having. The truck still runs. I have compression. I don't see any evidence of leaks on the ground. I was told it was the lifters, then another guy told me I had to get another engine. The headers are fine. Somebody else told me it was the pistons. Another guy he just didn't know. What do you think?