Recently my 300sd overheated due to a block heater leak. When I added anti freeze and water, I started back up, with no problem. Sounded normal. By the time I had driven the seven miles home at 60+ miles an hour, I developed a nailing noise. The guage still shows the compression to be up at 3 on the guage. It takes a little longer for the car to start, but it starts fine. Does not seem to run rough, but the noise stays the whole time, and increases frequency with acceleration. The noise seems to be coming from the top of the engine. I am going to work on it this weekend. Any ideas on what I should look for? Thanks

Bill Arndt