I bought an '87 SDL a few weeks ago. On the 5 hour trip home it had a terrible rattle. It wasn't diesel rattle. When I got it home I was able to isolate it to cylinder #2 by opening the nut on the top of the #2 injector. Every time I opened it the rattle went away. This was a very loud rattle so you could tell when it dropped out. I then removed the injector and the heat shield. I saw nothing out of the ordinary in there. Thinking that the engine probably was for the most part expired (bought it for the right fender and the hood, etc.) I put the heat shield and the injector back in and fired it up. Rattle was gone and hasn't shown back up. Runs quietly. I attribute it to extreme vibration in #2 injector line or the demon crawled out when I pulled the injector . It only made the noise at various rpms.