Have a '95 6.5L that has been making a slapping sound for about to months. took it to the mechanic twice. first he couldn't find anything thing and said that everything was good. The next time I took it in he located the noise in cylinder #1. He switched injector and the noise didnt go away but when he shut the cylinder off it did. he thought it was the pre-cup so I pulled the head and found that wasnt the problem. checked the valves to see if they were wore and they were fine and checked the lifters and they were fine also. Last winter the injection pimp was rebuilt. Do i need to dig into the block or just tear it a part and rebuild? trying to get it up and running before harvest.