I had an engine noise that started out this way. It would go away completely when the engine warmed up, initially. But over time, it got worse and no longer dissapeared as the engine came up to temp.
As the noise worsened, it started to sound like a rod bearing knock.
I had about 7500 miles on the engine by the time I pulled the pan and inspected and measured the bearing clearances, and found all of them to be fine.
It turned out to be a wrist pin bushing that had spun in the rod end. It took me forever to figure out what was the source of the noise, but I finally determined which hole it was in by removing the plug wires one at a time while the engine was running. When the noise was faint early on, I could not tell with the plug wire test where it was. But when it got loud and continuous, it was obvious.
Pete
